Methods and apparatus of providing transmit and/or receive diversity with multiple antennas in wireless communication systems

ABSTRACT

Transmit and/or receive diversity is achieved using multiple antennas. In some embodiments, a single transmitter chain within a wireless terminal is coupled over time to a plurality of transmit antennas. At any given time, a controllable switching module couples the single transmitter chain to one the plurality of transmit antennas. Over time, the switching module couples the output signals from the single transmitter chain to different transmit antennas. Switching decisions are based upon predetermined information, dwell information, and/or channel condition feedback information. Switching is performed on some dwell and/or channel estimation boundaries. In some OFDM embodiments, each of multiple transmitter chains is coupled respectively to a different transmit antenna. Information to be transmitted is mapped to a plurality of tones. Different subsets of tones are formed for and transmitted through different transmit chain/antenna sets simultaneously. The balance of tones allocated to the subsets for each antenna are changed as a function of predetermined information, dwell information, and/or channel condition feedback information.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/964,885 filed Oct. 14, 2004 now U.S. Pat. No. 7,039,370which claims the benefit of U.S. Provisional Patent Application Ser. No.60/511,965 filed Oct. 16, 2003.

FIELD OF THE INVENTION

The present invention relates to communications systems and, moreparticularly, to methods and apparatus for providing transmit and/orreceive diversity with multiple antennas in wireless communicationssystems.

BACKGROUND OF THE INVENTION

Channel fading is a ubiquitous and fundamental characteristic ofwireless communication systems. Fading deteriorates the link reliabilityof the wireless channel, thereby reducing system capacity and/ordegrading user service experience. Diversity is a well-known principlethat effectively combats wireless channel fading. The methods ofachieving diversity include utilizing space, angle, polarization,frequency, time, and multipath. Diversity can be achieved at thetransmitter and/or the receiver.

Consider the forms of diversity that can be realized by using multipleantennas at the transmitter and/or receiver of a wireless communicationsystem. These are grouped under the categories of transmit and receivediversity respectively.

FIG. 1 illustrates a simplified diagram of a receiver 100 in a prior artwireless system that is equipped with multiple antennas (receive antenna1 102, receive antenna N 102′) and exploits receive diversity. In thisreceiver 100, the multiple antennas (102. 102′) receive multipleversions of the same information-bearing signal. Assume that thewireless channel associated with any receive antenna is substantiallystatistically independent of the channel experienced by the otherantennas. Then, the probability of each of the receive antennas beingsimultaneously faded is significantly smaller than that of any receiveantenna being faded. Hence, the combined signal is much less likely tobe faded, thereby improving the link reliability. In practice, thereceive diversity gain is realized as follows. The signals received fromthe multiple receive antennas (102, 102′) are first individuallyprocessed with separate receive chains, each of which typically includesan analog signaling processing block (104, 104′), an analog-to-digitalconversion block (106, 106′), and a digital signal processing block(108, 108′), respectively. The processed signals (109, 109′) are thencombined in a combiner block 110. Combiner bock 110 may, for example,use selective combining or maximum ratio combining methods. The combiner110 outputs signal 112, which may be subjected to further signalprocessing.

Similarly, FIG. 2 illustrates a simplified diagram of a transmitter 200in a prior art wireless system equipped with multiple antennas (transmitantenna 1 202, transmit antenna N 202′) that exploits transmitdiversity. In the FIG. 2 transmitter 200 illustrated here, the sameinformation-bearing signal, source signal 204, is first split andpre-processed by splitter pre-processor 206 to generate multipletransmit signals (208, 208′), which are correlated with each other.These multiple transmit signals (208, 208′) are then individually passedthrough separate transmit chains including digital signal processingblocks (210, 210′), digital-to-analog conversion blocks (212, 212′),analog signal processing blocks (214, 214′) and transmitted withmultiple antennas (202, 202′), respectively.

Transmit diversity refers to the realization of diversity gain bysending multiple, correlated signals over a channel from thetransmitter. Typically, transmit diversity techniques make use ofmultiple transmit antennas to transmit these correlated signals.Firstly, transmit diversity is not straightforward to realize, ingeneral. Transmitting the same signal through multiple transmit antennastypically results in no diversity gain whatsoever.

One of the earliest transmit diversity techniques that was proposed isdelay diversity, in which the transmitter sends multiple copies of thesame information with different delays through different antennas. Amore sophisticated version of this scheme which uses two transmitantennas was proposed by Alamouti described in S. M. Alamouti, “A simpletransmitter diversity scheme for wireless communications,” IEEE Journalon Selected Areas in Communication, vol. 16, pp. 1451-1458, October1998.

Let the signal that is to be communicated be denoted by S(t) where t isassumed to be a discrete time instant. In the Alamouti scheme, twoconsecutive symbols are blocked off and transmitted over two timeinstants using the two antennas. Let X₁(t) and X₂(t) represent theoutput signals from the two antennas respectively, which may beexpressed as

$\begin{bmatrix}{X_{1}(t)} & {X_{1}\left( {t + 1} \right)} \\{X_{2}(t)} & {X_{2}\left( {t + 1} \right)}\end{bmatrix} = \begin{bmatrix}{S(t)} & {- {S^{*}\left( {t + 1} \right)}} \\{S\left( {t + 1} \right)} & {S^{*}(t)}\end{bmatrix}$

Suppose that the time-varying channel responses from the two transmitantennas, e.g., two base station transmit antennas, to the receiver,e.g., a mobile receiver, are denoted by h₁(t) and h₂(t) respectively.For simplicity of explanation we can assume a flat channel but the moregeneral case where the channel is frequency dependent can also behandled. If the channel coefficients are assumed to remain constant overtwo symbols, which is a mild assumption, the composite signal receivedby the mobile receiver can be represented byY(t)=h ₁ X ₁(t)+h ₂ X ₂(t)+W(t)Y(t+1)=h ₁ X ₁(t+1)+h ₂ X ₂(t+1)+W(t+1)which may be rewritten in terms of the original signal S(t) as

$\begin{bmatrix}{Y(t)} \\{Y\left( {t + 1} \right)}\end{bmatrix} = \begin{bmatrix}{{h_{1}{S(t)}} + {h_{2}{S\left( {t + 1} \right)}} + {W(t)}} \\{{{- h_{1}}{S^{*}\left( {t + 1} \right)}} + {h_{2}{S^{*}(t)}} + {W\left( {t + 1} \right)}}\end{bmatrix}$ ${{or}\mspace{14mu}{alternatively}},{\begin{bmatrix}{Y(t)} \\{Y^{*}\left( {t + 1} \right)}\end{bmatrix} = {{\begin{bmatrix}h_{1} & h_{2} \\h_{2}^{*} & {- h_{1}^{*}}\end{bmatrix}\begin{bmatrix}{S(t)} \\{S\left( {t + 1} \right)}\end{bmatrix}} + \begin{bmatrix}{W(t)} \\{W^{*}\left( {t + 1} \right)}\end{bmatrix}}}$

If the channel responses from the two transmit antennas to the receiverare known, it is straightforward to invert the transmitter codeconstruction and extract the transmitted signal by the followingtransformation:

$\begin{matrix}{\begin{bmatrix}{\hat{S}(t)} \\{\hat{S}\left( {t + 1} \right)}\end{bmatrix} = {\begin{bmatrix}h_{1}^{*} & h_{2} \\{- h_{2}} & h_{1}\end{bmatrix}\begin{bmatrix}{Y(t)} \\{Y\left( {t + 1} \right)}\end{bmatrix}}} \\{= {{\left( {{h_{1}}^{2} + {h_{2}}^{2}} \right)\begin{bmatrix}{S(t)} \\{- {S\left( {t + 1} \right)}}\end{bmatrix}} + {noise}}}\end{matrix}$which results in second-order diversity over a fading channel. TheAlamouti scheme is simple, but requires the receiver to track the gainsfrom each of the two transmit antennas separately, which normallyrequires two sets of pilots to be used. This is especially challengingin the cellular uplink, e.g., where a mobile device transmits to a basestation receiver. Furthermore, the requirement of known transmitdiversity techniques to use multiple transmitter chains, each of whichnormally includes both digital and analog signal processing blocks canbe cost prohibitive in many applications.

In view of the above discussion, there is a need for improved methodsand apparatus of achieving transmit and/or receive diversity in wirelesscommunications systems. Methods and apparatus that achieve diversitywhile reducing the amount of signaling dedicated to pilots over knownmethods would be beneficial. Methods and apparatus that achievediversity without the need for multiple transmit chains would also bebeneficial.

SUMMARY

Methods and apparatus for achieving transmitter and/or receiverdiversity in a wide variety of communications applications aredescribed. In various embodiments, transmit and/or receive diversity isachieved using multiple antennas. In some embodiments, a singletransmitter chain within a wireless terminal is coupled over time to aplurality of transmit antennas. At any given time, a controllableswitching module couples the single transmitter chain to one theplurality of transmit antennas. Over time, the switching module couplesthe output signals from the single transmitter chain to differenttransmit antennas. Switching decisions are based upon predeterminedinformation, dwell information, and/or channel condition feedbackinformation. Switching is performed on some dwell and/or channelestimation boundaries. In some OFDM embodiments, each of multipletransmitter chains is coupled respectively to a different transmitantenna. Information to be transmitted is mapped to a plurality oftones. Different subsets of tones are formed for and transmitted throughdifferent transmit chain/antenna sets simultaneously. The balance oftones allocated to the subsets for each antenna are changed as afunction of predetermined information, dwell information, and/or channelcondition feedback information.

While described with regard to many possible OFDM implementations, themethod and apparatus can be used with a wide variety of communicationstechniques including CDMA.

Numerous additional features, benefits and embodiments of the presentinvention are discussed in the detailed description which follows.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified diagram of receiver in a prior art wirelesssystem equipped with multiple antenna that exploits receive diversity.

FIG. 2 is a simplified diagram of a transmitter in a prior art equippedwith multiple antennas that exploits transmit diversity.

FIG. 3 is a drawing of an exemplary transmit chain and a plurality oftransmit antennas, implemented in accordance with the present invention.

FIG. 4 is a drawing illustrating exemplary downlink tone hopping in anexemplary OFDM system.

FIG. 5 is a drawing illustrating exemplary uplink tone hopping based ondwells in an exemplary OFDM system.

FIG. 6 is a drawing illustrating exemplary uplink tone hopping andantenna switching for an exemplary OFDM uplink system in which awireless terminal uses two different transmit antennas to achievetransmit diversity, in accordance with the present invention.

FIG. 7 is a drawing illustrating exemplary downlink tone hopping andantenna switching for an exemplary OFDM downlink system with twotransmit antennas, in accordance with the present invention.

FIG. 8 is a drawing of an exemplary receive chain and a plurality ofreceive antennas, in accordance with the present invention.

FIG. 9 is a drawing which illustrates an exemplary OFDM symbol includingmultiple tones, the multiple tones split between two transmit antennas,the multiple tones being transmitted simultaneously, in accordance withthe present invention.

FIG. 10 illustrates an exemplary variation of the tone-splittingillustrated in FIG. 9, in accordance with the present invention,including: changes in the tone-splitting over time, a full allocation oftones to first antenna and a zero allocation of tones to a secondantenna, and repetitive assignment of tone splitting.

FIG. 11 illustrates another exemplary variation of the tone-splittingillustrated in FIG. 9, in accordance with the present invention, iswhich the tone-splitting is varied in steps as function of channelquality feedback information.

FIG. 12 illustrates another exemplary variation of the tone-splittingillustrated in FIG. 9, in accordance with the present invention, inwhich the tone subsets associated with each antenna at any give timeinterval may be overlapping and the number of tones associated with eachsubsets changes as a function of channel quality feedback information.

FIG. 13 illustrates an exemplary communications system implemented inaccordance with the present invention and using methods of the presentinvention.

FIG. 14 illustrates an exemplary base station, implemented in accordancewith the present invention, which may use dwell boundary antennaswitching.

FIG. 15 illustrates another exemplary base station, implemented inaccordance with the present invention, which may use channel estimationboundary antenna switching.

FIG. 16 illustrates another exemplary OFDM base station, implemented inaccordance with the present invention, which may use assign differenttone subsets to different transmit antennas for simultaneoustransmission.

FIG. 17 illustrates an exemplary wireless terminal, implemented inaccordance with the present invention and using methods of the presentinvention including dwell boundary switching between multiple transmitantennas or antenna elements.

FIG. 18 illustrates another exemplary wireless terminal, implemented inaccordance with the present invention and using methods of the presentinvention including channel estimation boundary switching betweenmultiple transmit antennas or antenna elements.

FIG. 19 illustrates another exemplary wireless terminal, implemented inaccordance with the present invention and using methods of the presentinvention including assigning different tone subsets to differenttransmit antennas or antenna elements and simultaneously transmittingdifferent assigned tone subsets using the different antennas or antennaelements.

FIG. 20 is a drawing illustrating time divided into a sequence of timeintervals by an exemplary base station receiver, which maintainsseparate channel estimations from one time interval to another, inaccordance with the present invention.

FIG. 21 is a flowchart of an exemplary method of operating a wirelessterminal to communicate with a base station including performing dwellboundary switching of transmitter antenna elements, in accordance withthe present invention.

FIG. 22 is a flowchart of an exemplary method of operating a wirelessterminal to communicate with a base station including performing dwellboundary switching of transmitter antenna elements based on qualityindicator feedback information, in accordance with the presentinvention.

FIG. 23 is a flowchart of an exemplary method of operating a wirelessterminal to communicate with a base station including performing channelestimation boundary switching of transmitter antenna elements, inaccordance with the present invention.

FIG. 24 is a flowchart of an exemplary method of operating a wirelessterminal to communicate with a base station including performing channelestimation boundary switching of transmitter antenna elements based onquality indicator feedback information, in accordance with the presentinvention.

FIG. 25 is a flowchart of an exemplary method of operating an OFDMcommunication device including assigning different tone subsets todifferent antenna elements and transmitting over multiple antennaelements in parallel, in accordance with the present invention.

FIG. 26 is a flowchart of an exemplary method of operating an OFDMcommunications device including receiving and processing channel qualityindicator information, assigning different tone subsets to differentantenna elements, and transmitting over multiple antenna elements inparallel, in accordance with the present invention.

FIG. 27 is a drawing illustrating an exemplary transmitter configurationwhich may be used in tone-splitting embodiments of the presentinvention.

FIG. 28 is a drawing illustrating an exemplary variation of thetransmitter configuration of FIG. 27 including commonality in thedigital section, in accordance with the present invention.

FIG. 29 is a drawing illustrating another variation of the transmitterconfiguration of FIG. 27, including only two transmit chains, an antennaswitching module, and more than two transmitter antennas, in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the principle of diversity helps to improve the wireless linkreliability, the use of multiple transmit and/or receive chainsincreases the cost and complexity of the transmitter and/or receiver.Typically, in a wireless communications system, there are many wirelessterminals for each base station deployed. The wireless terminals may be,e.g., consumer owned and operated portable battery powered mobiledevices such as cell phones or cellular data communication devices. Theincreased cost and complexity are particularly important considerationsat the wireless terminal, e.g., mobile node, side. Various aspects andfeatures of the present invention are directed to wireless systemsequipped with multiple antennas that can achieve diversity with aminimal increase in cost and/or complexity.

Various aspects of providing transmit diversity, in accordance with thepresent invention, shall now be described. In accordance with variousembodiments of the invention, transmit diversity can be achieved in awireless communication system by employing a single transmit chain andby switching between multiple transmit antennas.

FIG. 3 is a drawing 300 including an exemplary transmit chain 302 inaccordance with the present invention. The exemplary transmit chain 302includes a digital signal processing block 304, a digital-to-analogconversion block 306, an analog signal processing block 308, and aswitching module 310. An input signal 303 is input to the digital signalprocessing block 304. The digital signal processing block 304encompasses and performs digital domain signal processing functions,such as encoding, modulation and digital filtering. The digital signalprocessing block 304 typically includes a baseband digital chain. Anoutput digital signal 305 from the digital signal processing block 304is input to the digital-to-analog conversion block 306. Thedigital-to-analog conversion block 306 converts digital signal 305 toanalog signal 307, which becomes the input to the analog signalprocessing block 308. The analog signal processing block 308 encompassesand performs analog domain signal processing functions, such asup-conversion to carrier frequency, analog filtering and poweramplification. The analog signal processing block 308 typically includesa baseband analog chain and RF analog chain. The output of the analogsignal processing block 308 is then routed via switching module block310 as output signal (311 or 311′) and then transmitted through one ofthe plurality of transmit antennas (transmit antenna 1 312 or transmitantenna N 312′), respectively. The switching module block 310 determineswhich transmit antenna (312, 312′) to be used at any given time. Fromtime to time, the switching module block 310 chooses to use differenttransmit antennas (312, 312′), and directs the output 309 of the analogsignal processing block 308 to the chosen transmit antenna (312 or312′).

The switching module 310 is controlled by signals received from aswitching control module 318. Channel feedback information 314 from thebase station is input to an uplink channel feedback module 316. Theuplink channel feedback module 316 determines which transmit antenna(312, 312′) results in better channel quality and forward thatinformation to the switching control module 318. In addition, dwellinformation 320, e.g., dwell boundary information, is input to theswitching control module 318. The switching control module can use thereceived information to make decisions regarding antenna selection. Forexample, the switching control module 318, can control switching ondwell boundaries. In some embodiments, the switching control module 318alternates between antennas as a function of the dwell number and thenumber of antennas. In some embodiments, the switching control modulecan choose, based upon channel quality estimate information, to eitheruse the antenna associated with the better channel quality exclusivelyor use that antenna more often than others. In some embodiments, anuplink channel feedback module 314 is not used and switching iscontrolled based upon dwell information 320 without using channelfeedback information 314.

Note that although there are multiple physical transmit antennas (312,312′), the transmitter 300 uses a single transmit chain 302. This isvery different from the prior art system illustrated in FIG. 2, whichemploys multiple transmit chains, each used for one transmit antenna(202, 202′).

Let N denote the number of the transmit antennas. Let {H_(k), k=1, . . ., N} denote the wireless channel response from each of the transmitantennas to the receiver. The transmit antennas are, in someembodiments, spatially arranged in such a manner that the ensemble ofchannel responses, {H_(k)}, are substantially independent. By switchingfrom one transmit antenna to another, the effective channel responsefrom the transmitter to the receiver varies among {H_(k)}, thereforerealizing transmit diversity. For example, suppose N=2. Suppose that theswitching block chooses to use the transmit antenna 1 from time t1 tot2, and to use the transmit antenna 1 from time t2 to t3. Suppose that acoding block is transmitted in the time interval from t1 to t3. Then,part of the coding block experiences the channel response H₁ and theremaining experiences the channel response H₂. Hence, assuming H₁ and H₂are independent, the coding block may see the benefit of thesecond-order diversity. This is especially true when low code rates(below ½ in this case) are used.

In various embodiments of the present invention, it is useful for thereceiver to be aware of the time instants when the transmitter switchesantennas. This may be important, for example, when the receivermaintains different channel estimates corresponding to the differentantennas, and evolves the appropriate channel estimate in any particularantennas transmit duration.

For the sake of illustration, consider the invention in the context ofthe spread spectrum orthogonal frequency division multiplexing (OFDM)multiple-access system. Note that the present transmit diversitytechnique is applicable to other systems, e.g., code division multipleaccess (CDMA) systems, as well.

In the exemplary OFDM system, tones hop to realize spread spectrumadvantages. In the downlink, from the base station to the wirelessterminal, tones hop every OFDM symbol. Each logical tone is mapped to adifferent physical tone and this mapping is varied on every OFDM symbolboundary as illustrated in FIG. 4. FIG. 4 is a drawing 400 of frequencyon the vertical axis 402 vs time on the horizontal axis 404 illustratingexemplary OFDM downlink tone hopping. The basic unit on the frequencyaxis is a physical tone 406, while the basic unit on the horizontal axis404 is an OFDM symbol duration 408. An exemplary logical tone beinghopped to different physical tones and being varied on every OFDM symbolboundary is illustrated by the sequence of squares (410, 412, 414, 416,418, 420, and 422) which illustrates changes in the physical toneposition on each OFDM symbol boundary. This hopping facilitates that acoding block including some subset of logical tones is spread across theavailable frequency band.

In the uplink, from the wireless terminal to the base station, everylogical tone is mapped to a physical tone with the mapping held constantfor a few OFDM symbol periods. This duration is known as a dwell period.The process of uplink hopping across dwell periods is illustrated inFIG. 5. FIG. 5 is a drawing 500 illustrating frequency on the verticalaxis 502 vs time on the horizontal axis 504 and is used for illustratingexemplary uplink tone hopping. The basic unit on the vertical axis 502is the physical tone; area 506 shows several, e.g., two, exemplarycontiguous physical tones. The basic unit on the horizontal axis 504 isan OFDM symbol duration 508. Each OFDM dwell duration 510 includes foursuccessive OFDM symbol durations. In other embodiments, a dwell durationmay include a different number of OFDM symbol durations, e.g., sevenOFDM symbol durations. FIG. 5 shows four successive OFDM dwellintervals: dwell 1 512, dwell 2 514, dwell 3 516, and dwell 4 518. Asshown in FIG. 5, logical tones are mapped to physical tones with themapping held constant for four successive OFDM symbol durations;represented by tone set 520 during dwell 1 512, tone set 522 duringdwell 2 514, tone set 524 during dwell 3 516, and tone set 526 duringdwell 4 518.

Various embodiments of the present invention can be used at thetransmitter of the wireless terminal to achieve transmit diversity inthe cellular uplink. An exemplary embodiment, in accordance with thepresent invention, switches the transmit antennas at the dwellboundaries of the uplink signal. That is, suppose dwell 1 512 and dwell2 514 are two successive dwells. Then, the switching block chooses touse one transmit antenna in dwell 1 512 and to switch to anothertransmit antenna in dwell 2 514. The transmitter may switch the antennaonce every dwell or once every few dwells. For example, FIG. 6 shows adrawing 600 illustrating exemplary uplink tone hopping and antennaswitching for an exemplary OFDM uplink system with two transmitantennas. Drawing 600 includes a graph of frequency on vertical axis 602vs time on horizontal axis 604. The basic unit of frequency is tone 606.The basic unit of time is OFDM symbol duration 608, and an OFDM dwellduration 610 includes four successive OFDM symbol durations 608. Logicaltones are frequency hopped to physical tones and the hopping changes ondwell boundaries. For example, during (dwell 1 612, dwell 2 614, dwell 3616, dwell 4 618), physical tone (620, 622, 624, 626) is used. In FIG.6, the signal in the odd dwells (612, 616) is transmitted throughantenna 1 628 and that in the even dwells (614, 618) is transmittedthrough antenna 2 (630). Assume that the base station receiver does notassume any channel coherence from one dwell to another. For example, thereceiver may not carry out channel estimation across dwells. Then,switching transmit antennas at the dwell boundaries does not affect theoperations carried out at the receiver. Indeed, in this situation, thereceiver may not even be aware of the use of the present transmitdiversity invention. If a coding block is transmitted over a timeinterval of a few dwells, then the coding block may see the benefit ofsecond-order diversity, especially for low code rates.

Similarly, the various features of the invention can be used at the basestation to achieve transmit diversity in the cellular downlink. In someembodiments of the present invention, the base station switches thetransmit antennas once every few OFDM symbols, and the wireless terminalknows when antenna switching occurs. FIG. 7 shows a drawing 700illustrating exemplary downlink tone hopping and antenna switching foran exemplary OFDM downlink system with two transmit antennas. Drawing700 includes a graph of frequency on vertical axis 702 vs time onhorizontal axis 704. The basic unit of frequency is tone 706. The basicunit of time is OFDM symbol duration 708. Logical tones are frequencyhopped to physical tones and the hopping changes for successive OFDMsymbol durations. FIG. 7 illustrates an exemplary logical tone for oneOFDM symbol duration being hopped to different physical tones asillustrated by the sequence of squares (718, 720, 722, 724, 726, 728,730, 732, 734, 736, 738, 740, 742, 744, 746, 748). FIG. 7 may correspondto an exemplary OFDM downlink system with two transmit antennas (antenna1 750 and antenna 2 752), where switching antennas occurs once every 4OFDM symbols. For example, the signal in time intervals (710, 714)denoted A is transmitted through antenna 1 750, and that in timeintervals (712, 716) denoted B is transmitted through antenna 2 752. Thewireless terminal receiver maintains two separate channel estimates. Thefirst channel estimate is trained and used in the time intervals A (710,714), while the second channel estimate is trained and used in the timeintervals B (712, 716).

In the above exemplary descriptions, the switching block at thetransmitter chooses each of the transmit antennas substantially equally.Now suppose, in some embodiments of the present invention, that thereceiver feeds back some indication of the channel quality to thetransmitter. Then in a slow time-varying environment, the transmittercan find out which transmit antenna results in better channel qualityand choose to either use that antenna exclusively or use that antennamore often than others.

As a practical matter, in radio frequency (RF) transmit circuits, thereis usually a transient response associated with switching antennas. Theuse of the cyclic prefix in the exemplary OFDM system can effectivelyabsorb the antenna transient response and maintain the basic propertiesof the OFDM system, such as orthogonality.

This invention realizes transmit diversity gains without the need formultiple transmit chains. There is no explicit pre-processing of thesignal involved, e.g., in space-time codes, which requires thetransmitted information signals over the different antennas to bedifferent. There are other advantages conferred by various embodimentsof the present invention. Most transmit diversity schemes require theuse of different pilots in the signals transmitted by the differentantennas in order that the receiver may track the channel responsesseparately. Various embodiments of the present invention obviate theneed for multiple pilots since the same information signal istransmitted through different antennas at different times.

Various aspects of providing receive diversity, in accordance with thepresent invention, shall now be described. In accordance with theinvention, receive diversity can be achieved in a wireless communicationsystem by employing a single receive chain and by switching betweenmultiple receive antennas.

FIG. 8 shows a drawing 800 of an exemplary receive chain 802 and aplurality of receive antennas (receive antenna 1 812, receive antennaN), in accordance with the invention. Exemplary receive chain 802includes a switching module 810, an analog signal processing block 808,an analog-to-digital conversion block 806, and a digital signalprocessing block 804. The switching module block 810 determines whichreceive antenna (812, 812′) to be used at any given time. For time totime, the switching module block 810 chooses to use different receiveantennas, and directs signal (811, 811′) from the chosen receive antenna(812, 812′), respectively, to the input 809 of the analog signalprocessing block 808. The input 809 of the analog signal processingblock 808 can come from one of the receive antennas (812, 812′). Theanalog signal processing block 808 encompasses and performs analogdomain signal processing functions, analog filtering, low-noiseamplification, and down-conversion to baseband. The analog signalprocessing block 808 typically includes baseband analog chain and a RFanalog chain. The output of the analog signal processing block 808 issignal 807. The analog-to-digital-conversion block 806 converts theoutput 807 of the analog signal processing block 808 to a digital signal805, which becomes the input of the digital signal processing block 804.The digital signal processing block 804 encompasses and performs digitaldomain signal processing functions, such as digital filtering, decoding,and demodulation. The digital signal processing block 804 typicallyincludes a baseband digital chain. The output of digital signalprocessing block 804 is digital signal 803.

Note that although there are multiple receive antennas (812, 812′), thewireless system has a single receive chain 802. This is very differentfrom the prior art system illustrated in FIG. 1, which employs multiplereceive chains, each used for one receive antenna.

Various features of the present invention can be used at the wirelessterminal to achieve downlink receive diversity. In an exemplaryembodiment, an exemplary wireless terminal, with two receive antennas,switches the receive antennas once every few OFDM symbols. Thisembodiment is very similar to the embodiment of this invention whichswitches transmit antennas at the base station, which is shown in FIG.7. In particular, the signal in time intervals A (710, 714) is receivedthrough receive antenna 1 812, and that in time intervals B (712, 716)is received through antenna 2 812′. The wireless terminal receivermaintains two separate channel estimates, trained and used in the timeintervals A and B, respectively.

Similarly, features of the invention can be used at the base station toachieve uplink receive diversity. An exemplary embodiment is to switchthe receive antennas at the dwell boundaries of the uplink signal. Theembodiment is very similar to that which employs switching of transmitantennas at the wireless terminal transmitter, which is shown in FIG. 6.In particular, consider an exemplary base station with two receiveantennas; the signal in the odd dwells (612, 616) is received throughreceive antenna 1 812 and that in the even dwells (614, 618) is receivedthrough receive antenna 2 812′. Assuming that the receiver does notassume any channel coherence from one dwell to another, switchingreceive antennas at the dwell boundaries does not affect the operationscarried out at the receiver.

In the above description, the switching module block 810 chooses each ofthe receive antennas substantially equally. This switching may be underprocessor control or preconfigured to occur in a specific manner orsequence. Now suppose that the receiver estimates the channel quality.Then, the receiver can find out which receive antenna results in betterchannel quality and choose to either use that antenna exclusively or usethat antenna more often than others.

Note that this invention may be used in combination with other methodsof realizing diversity. For example, consider a wireless system in whichthe transmitter at the wireless terminal uses two switched antennas asdescribed in this invention. The base station receiver uses traditionalmaximal ratio combining with two antennas. Together, this realizesfourth-order diversity in the cellular uplink.

Tone-splitting shall now be described in the context of the presentinvention. The orthogonality properties of tones in exemplary spreadspectrum OFDM (orthogonal frequency division multiplexing)multiple-access systems enable a unique method of obtaining transmitdiversity gains. Consider drawing 900 of FIG. 9, which illustrates anexemplary OFDM symbol 904 including multiple tones (tone 0 906, tone 1908, tone 2 910, tone 3 912, tone 4 914, tone 5 916, tone 6 918, tone 7920) being transmitted through two antennas (antenna 1 922, antenna 2926) as signals (924, 928), respectively. The tones of the symbol whichare shaded (908, 912, 916, 920) are transmitted through transmit antenna1 922, while those marked with clear boxes (906, 910, 914, 918) aretransmitted using transmit antenna 2 926. This may allow second-ordertransmit diversity, especially for low code-rates since the coded blockis distributed across several OFDM symbols. Half the modulation symbolsin the coded block are transmitted through each of the antennas(922,926). Extensions of this transmit diversity method to multipletransmit antennas are straightforward.

Drawing 1000 of FIG. 10 illustrates a variation of the tone-splittingdescribed in FIG. 9, in accordance with the present invention. FIG. 10includes a plot of frequency, represented by tone index number rangingfrom 0 . . . 7, on the vertical axis 902 vs time on the horizontal axis1003. The basic units of the time axis are OFDM symbol times. ExemplaryOFDM symbols (1004, 1006, 1008, 1010, 1012, 1014, 1016, 1017) eachinclude multiple tones (tone 0 1018, tone 1 1020, tone 2 1022, tone 31024, tone 4 1026, tone 5 1028, tone 6 1030, tone 7 1030) beingtransmitted through two antennas (antenna 1 1034, antenna 2 1036) assignals (1038, 1040), respectively. The tones of the each OFDM symbolwhich are shaded are transmitted through transmit antenna 1 1034, whilethose identified with clear boxes are transmitted using transmit antenna2 1036. Each tone in each OFDM symbol transmits a modulation symbolconveying encoded information. Initially, for the first four OFDM symboltime intervals (1004, 1006, 1008, 1010), half of the modulation symbolsare transmitted through antenna 1 1034 and half through antenna 2 1036.Then, the communicating device decides to emphasize antenna 1 1034. Forexample, feedback information to the communications device may haveindicated that the channel from antenna 1 to a receiver is better thanthe channel from antenna 2 to a receiver, e.g., based upon receivedpower levels and/or based upon ack/nak information. The communicationsdevice changes the number of tones assigned to each antenna. Duringinterval 1012, antenna 1 1034 receives the full set of tones, whileantenna 2 receives 0 tones to use for transmission. During the nextinterval 1014, each antenna receives half of the tones to use fortransmission. This pattern of alternating between tone allocation dutycycles repeats until a decision is made to change the balance betweenantennas 1034, 1036. In some embodiments, the basic unit of time is aninterval comprising several consecutive OFDM symbol times. In someembodiments, e.g., where the communications device is a wirelessterminal and the communications device transmits uplink signals to abase station, the basic unit of time is a dwell comprising severalconsecutive OFDM symbol times.

Drawing 1100 of FIG. 11 illustrates another variation of thetone-splitting described in FIG. 9, in accordance with the presentinvention. FIG. 11 includes a plot of frequency, represented by toneindex number ranging from 0 . . . 7, on the vertical axis 1102 vs timeon the horizontal axis 1103. The basic units of the time axis are OFDMdwells. Exemplary OFDM dwells (1104, 1106, 1108, 1110, 1112, 1114, 1116)each include multiple tones (tone 0 1118, tone 1 1120, tone 2 1122, tone3 1124, tone 4 1126, tone 5 1128, tone 6 1130, tone 7 1132) beingtransmitted through two antennas (antenna 1 1134, antenna 2 1136) assignals (1138, 1140), respectively. The tones of the each OFDM dwellwhich are shaded are transmitted through transmit antenna 1 1134, whilethose identified with clear boxes are transmitted using transmit antenna2 1136. Each tone in each OFDM dwell transmits a set of modulationsymbol, e.g., one modulation symbol for each OFDM symbol time intervalin the dwell, the modulation symbols conveying encoded information.Initially, for the first three OFDM dwells (1104, 1106, 1108), half ofthe modulation symbols are transmitted through antenna 1 1134 and halfthrough antenna 2 1136. Then, the communicating device decides toemphasize antenna 1 1134, and changes the tone balance to slightly favorantenna 1 for dwell 1110. For example, feedback information to thecommunications device may have indicated that the channel from antenna 11134 to a base station receiver is better than the channel from antenna2 1136 to the base station receiver, e.g., based upon received powerlevels and/or based upon ack/nak information. The communications devicecontinues to monitor feedback information and make adjustments to thetone balance between antennas as observed by the changes from exemplarydwells 1110 to 1112, 1112 to 1114, and 1114 to 1116. In someembodiments, changes are not performed on dwell boundaries, but ratheron a given number of OFDM symbol times or on channel conditionmeasurement boundaries.

In the examples illustrated in FIGS. 9 and 10, the tones assigned to theantennas are mutually exclusive, at any given time. However, in variousembodiments of the present invention, the subsets of tones assigned toeach antenna can include overlapping subsets of tones. Drawing 1200 ofFIG. 12 illustrates another variation of the tone-splitting described inFIG. 9, in accordance with the present invention. FIG. 12 includes aplot of frequency, represented by tone index number ranging from 0 . . .7, on the vertical axis 1202 vs time on the horizontal axis 1203. Thebasic units of the time axis are OFDM dwells. Exemplary OFDM dwells(1204, 1206, 1208, 1210, 1212, 1214, 1216) each include multiple tones(tone 0 1218, tone 1 1220, tone 2 1222, tone 3 1224, tone 4 1226, tone 51228, tone 6 1230, tone 7 1232) being transmitted through two antennas(antenna 1 1234, antenna 2 1236) as signals (1238, 1240), respectively.The tones of the each OFDM dwell which are shaded by diagonal linesincreasing from left to right are transmitted through transmit antenna 11234, while those tones shaded by diagonal lines decreasing from left toright are transmitted using transmit antenna 2 1236. Note that inexemplary OFDM dwells 1204 and 1216, representing a balance conditionbetween the two antennas (1234, 1238), three tones (tone 0 1218, tone 11220, and tone 2 1222) are transmitted using antenna 1 1234 exclusively,three tones (tones 5 1228, tone 6 1230, and tone 7 1232) are transmittedusing antenna 2 1236 exclusively, and 2 tones (1224 and 1226) aretransmitted by both of the antennas (1234 and 1236). Each tone in eachOFDM dwell is used to transmit a set of modulation symbols, e.g., onemodulation symbol for each OFDM symbol time interval in the dwell, themodulation symbols conveying encoded information. As the communicatingdevice decides to emphasize antenna 2 1236, it changes the tone balanceto favor antenna 2 as observed in dwells 1206, 1208, 1210, 1212, and1214. The amount of tone imbalance is adjusted, e.g., from dwell todwell. For example, feedback information to the communications devicemay have indicated that the channel from antenna 2 to a receiver isbetter than the channel from antenna 1 to a receiver, e.g., based uponreceived power levels and/or based upon ack/nak information, and thedegree of channel quality difference is used to decide the level of toneimbalance. In some embodiments, changes are not performed on dwellboundaries, but rather on a given number of OFDM symbol times or onchannel condition measurement boundaries.

Although tone hopping has not been illustrated in the examples of FIGS.10-12, for simplicity of illustration, it is to be understood that inmany embodiments the tones are hopped from one OFDM symbol duration tothe next OFDM symbol duration on the downlink or from one dwell to thenext dwell on the uplink. In addition, the tones associated with onetransmit antenna at any one given time may form a subset of tones, thesubset of tones being a disjoint set of tones. This method of realizingtransmit diversity, by employing tone splitting techniques, usesmultiple transmit chains.

FIG. 13 illustrates an exemplary communications system 10 implemented inaccordance with the invention, e.g., to achieve benefits of transmitand/or receive diversity using multiple antennas or antenna elements.Exemplary system 10 includes a plurality of cells (cell 1 (2), cell M(2′)). Each cell (cell 1 (2), cell M (2′)) represents a wirelesscoverage area for a base station (BS 1 (12), BS 2 (12′)), respectively.System 10 also includes a network node 3 coupled to the base stations(BS 1 (12), BS 2 (12′)) via network links (4, 4′), respectively. Thenetwork node 3, e.g., a router, is also coupled to the Internet andother network nodes via network link 5. The network links (4, 4′, 5) maybe, e.g., fiber optic links. Each cell includes a plurality of wirelessterminals that are coupled to the cell's base station via wirelesslinks, and if the wireless terminals are mobile devices they may movethroughout the system 10. In cell 1 (2), multiple wireless terminals (WT1 (14), WT N (16)), shown as mobile nodes (MN 1 (14) through MN N (16)),communicate with base station 1 (12) through the use of communicationsignals (13, 15), respectively. In cell M (2′), multiple wirelessterminals (WT 1′ (14′), WTN′ (16′)), shown as mobile nodes (MN 1′ (14′)through MN N′ (16′)), communicate with base station M (12′) through theuse of communication signals (13′, 15′), respectively. Each mobileterminal may correspond to a different mobile user and are thereforesometimes referred to as user terminals. The signals (13, 15, 13′, 15′)may be, e.g., orthogonal frequency division multiplexing (OFDM) signals.In some embodiments the signals (13, 15, 13′, 15′) may be, e.g., codedivision multiple access (CDMA) signals. The base stations (12, 12′) andwireless terminals (MN1, MN N, MN 1′, MN N′) (14, 16, 14′, 16′) eachimplement the method of the present invention. Thus, signals (13, 15,13′, 15′) include signals of the type discussed in this application,which are transmitted in accordance with the invention.

FIG. 14 illustrates an exemplary base station—access node 1400,implemented in accordance with the invention. Base station 1400 may beany of the exemplary base stations 12, 12′ of FIG. 13. The base station1400 includes receiver chain/antenna module 1402 and transmitterchain/antenna module 1404. The receiver chain/antenna module 1402 may beimplemented similarly to or the same as shown in FIG. 8. The transmitterchain/antenna module 1404 may be implemented similarly to that shown inFIG. 3, but with switching control a function of OFDM timing structureinformation, predetermined information, and/or downlink channel feedbackinformation from WTs. The receiver chain/antenna module 1402 includes areceive antenna or antenna element 1406 and a receive chain 1410. Module1402, in some embodiments, includes multiple antennas or antennaelements (receive antenna 1 1406, receive antenna N 1408) and itsreceiver chain 1410 includes a dwell boundary controllable switchingmodule 1412, e.g. switching circuitry. The transmitter chain/antennamodule 1404 includes a transmit antenna or antenna element 1414 and atransmitter chain 1418. In some embodiments, module 1404 includesmultiple antennas or antenna elements (transmit antenna 1 1414, transmitantenna N 1416) and its transmitter chain 1418 includes a controllableswitching module 1420. The receiver module 1402 receives uplink signalsfrom WTs including uplink signals transmitted from different WT transmitantennas or antenna elements of the same WT during different dwells. Thetransmitter module 1404 transmits downlink signals to the WTs includingchannel quality indicator feedback signals indicative of the received WTuplink signals. The modules 1402, 1404 are coupled by a bus 1422 to anI/O interface 1424, processor 1426, e.g., CPU, and memory 1428. The I/Ointerface 1426 couples the base station 1400 to the Internet and toother network nodes, e.g., routers, other base stations, AAA nodes, etc.The memory 1428 includes routines 1430 and data/information 1432. Theprocessor 1426 executes the routines 1430 and uses the data/information1432 in memory 1428 to cause the base station 1400 to operate inaccordance with the invention.

Routines 1430 includes communications routines 1434 used for controllingthe base station 1400 to perform various communications operations andimplement various communications protocols. The routines 1430 alsoincludes a base station control routine 1436 used to control the basestation 1400 to implement the steps of the method of the presentinvention. The base station control routine 1436 includes a schedulermodule 1438 used to control transmission scheduling and/or communicationresource allocation, e.g., the assignment of uplink and downlink segmentto WTs. Base station control routine 1436 also includes, in someembodiments, e.g., those including dwell boundary switching module 1412and multiple receive antennas (1406, 1408), a receiver antenna switchingcontrol module 1440. Base station control routines 1436 also includes,in some embodiments, e.g., those including switching module 1420 andmultiple transmit antennas (1414, 1416), a transmitter antenna switchingcontrol module 1442. The switching devices 1412 in this receiver chain1410 and 1420 in the transmitter chain 1418, when implemented, areresponsive to control signals generated by the processor 1426 whenoperating under direction of these modules (1440, 1442), respectively.The control signals cause switching between antennas or antenna elementsin accordance with the invention. The receiver antenna switching controlmodules 1440 may use the data/information 1432 including the uplinkquality indicator feedback information 1458, dwell information 1478, andreceiver antenna switching information 1472 in making antenna switchingdecisions. The transmitter antenna switching control module 1442 may usethe data/information 1432 including the OFDM symbol timing information1476, received downlink channel feedback report information 1459, andtransmitter antenna switching information 1474 in making antennaswitching decisions.

Base station control routine 1436 also includes uplink channel feedbackmodule 1444 which controls the evaluation of received uplink signals,generation, and transmission of channel quality indicator feedbacksignals such as feedback messages 1464 including WT power controlfeedback information 1460 and transmission acknowledgment/negativeacknowledgement (ack/nak) feedback information 1462 indicating thesuccess or failure in receipt of an uplink signal or signals.

Memory 1428 also includes data/information 1432 used by communicationsroutines 1434 and control routine 1436. Data/information 1432 includesWT data/information 1446 and system information 1448. WTdata/information 1446 includes a plurality of sets of WT information (WT1 data/information 1450, WT N data/information 1452). WT 1data/information 1450 includes user/device/session/resource information1454, timing synchronization information 1456, uplink quality indicatorfeedback message information 1458, and received downlink channelfeedback report information 1459. User/device/session/resourceinformation 1454 includes user/device identification information,session information such as peer node information and routinginformation, and resource information such as uplink and downlinktraffic channel segments assigned by the scheduler 1438 to WT1. Timingsynchronization information 1456 includes information to synchronize WT1timing with respect to BS timing, e.g., adjustment information tocompensate for propagation delays. Uplink quality indicator feedbackmessage information 1458 includes WT power control information 1460,ack/nak information 1462, and feedback messages 1464. Received downlinkchannel feedback report information 1459 includes information obtainedfrom a received downlink channel feedback report transmitted by WT1 inresponse to downlink pilot broadcast signals transmitted by BS 1400.System information 1448 includes timing information 1466, toneinformation 1468, tone hopping sequence information 1470, optionallyreceiver antenna switching information 1472, and optionally transmitterantenna switching information 1474. Timing information 1466 includesOFDM symbol timing information, e.g., the time interval to transmit anOFDM symbol, synchronization information relative to the OFDM symbolintervals, timing information corresponding to grouping of OFDM symbolintervals such as superslots, beaconslots, and ultraslots, and/or timinginformation corresponding to fixed number of OFDM symbol intervals fortransmission before switching between transmit antennas or antennaelements. Timing information 1466 also includes dwell information 1478,e.g., the grouping of a number of successive OFDM symbol intervals inwhich the logical to physical tone hopping is held constant during thatinterval for uplink signals. The tones used for uplink signaling arehopped differently from one dwell to the next dwell according to anuplink hopping sequence. Dwell information 1478 includes dwell boundaryinformation 1480. The dwell boundary information 1478, in accordancewith the invention, determines the time at which the WT can performtransmitter antenna switching. In some embodiments, the BS receivermodule 1402 also performs dwell boundary switching operations betweenantennas and uses dwell boundary information 1480. Tone information 1468includes sets of tones used for uplink and downlink signals, and subsetsof tones assigned to specific segments at specific times. Tone hoppingsequence information 1470 includes downlink tone hopping sequenceinformation, e.g., where the tones are frequency hopped for successiveOFDM symbol times and uplink tone hopping sequence information, e.g.,where the tones are frequency hopped for successive dwells. Receiverantenna switching information 1472 includes information such ascriteria, predetermined switching sequences, antenna element utilizationinformation, and antenna element control information used by thereceiver antenna switching control module 1440. Transmitter antennaswitching information 1474 includes information such as criteria,predetermined switching sequences, antenna element utilizationinformation, and antenna element control information used by thetransmitter antenna switching control module 1442.

In some systems, the base station receiver estimates the uplink channelof a wireless terminal in order to demodulate the signal received fromthat wireless terminal. The operation of channel estimation oftendepends on the structure of the received signal. Take an OFDM system asan example, where the tones of the uplink signal hop every few OFDMsymbols. From one hop to another, the frequency location of tones may beassumed to be randomized. In such a case, the base station receiver mayassume that the channel estimation changes dramatically from one hop toanother, and as a result, may discard the memory of the channelestimation in a previous hop and carry out the channel estimationoperation starting from the scratch during a new hop. In the case of anexemplary, CDMA system, the base station receiver may divide the timeinto a sequence of time intervals, as shown in FIG. 20, and maintainseparate channel estimation from one time interval to another. Drawing2000 of FIG. 20 shows a horizontal axis 2002 representing time which hasbeen divided into an exemplary sequence of time intervals: A2 2004, B12006, A1 2008, B 2010, A 2012. For example, the channel estimation oftime interval A 2012 is not based on the signal received in timeinterval B 2010. In this case, the time instant between time intervals Aand B is called the channel estimation boundary 2014. In one embodiment,the channel estimation of time interval A 2012 may be independent of thereceived signal in any of the preceding time intervals, in which case,the channel estimation is solely based on the signal received in timeinterval A 2012. In another embodiment, the channel estimation of timeinterval A 2012 may be based on the received signal in the precedingtime intervals A1 2008, A2 2004, and so on.

FIG. 15 illustrates another exemplary base station—access node 1800,implemented in accordance with the invention. Base station 1800 may beany of the exemplary base stations (12, 12′) of FIG. 13. The basestation 1800 includes receiver chain/antenna module 1802 and transmitterchain/antenna module 1804. The receiver chain/antenna module 1802 may beimplemented similarly to or the same as shown in FIG. 8. The transmitterchain/antenna module 1804 may be implemented similarly to that shown inFIG. 3, but with the switching control a function of channel estimationboundary information and/or downlink channel feedback information fromWTs. The receiver chain/antenna module 1802 includes a receive antennaor antenna element 1806 and a receive chain 1810. Module 1802, in someembodiments, includes multiple antennas or antenna elements (receiveantenna 1 1806, receive antenna N 1808) and its receiver chain 1810includes a channel estimation boundary controllable switching module1812, e.g. switching circuitry. The transmitter chain/antenna module1804 includes a transmit antenna or antenna element 1814 and atransmitter chain 1818. In some embodiments, module 1804 includesmultiple antennas or antenna elements (transmit antenna 1 1814, transmitantenna N 1816) and its transmitter chain 1818 includes a controllableswitching module 1820. The receiver module 1802 receives uplink signalsfrom WTs including uplink signals transmitted from different WT transmitantennas or antenna elements of the same WT during different intervalscorresponding to different base station channel estimations. Thetransmitter module 1804 transmits downlink signals to the WTs includingchannel quality indicator feedback signals indicative of the received WTuplink signals. The modules 1802, 1804 are coupled by a bus 1822 to anI/O interface 1824, processor 1826, e.g., CPU, and memory 1828. The I/Ointerface 1824 couples the base station 1800 to the Internet and toother network nodes, e.g., routers, other base stations, AAA nodes, etc.The memory 1828 includes routines 1830 and data/information 1832. Theprocessor 1826 executes the routines 1830 and uses the data/information1832 in memory 1828 to cause the base station 1800 to operate inaccordance with the invention.

Routines 1830 includes communications routines 1834 used for controllingthe base station 1800 to perform various communications operations andimplement various communications protocols. The routines 1830 alsoincludes a base station control routine 1836 used to control the basestation 1800 to implement the steps of the method of the presentinvention. The base station control routine 1836 includes a schedulermodule 1838 used to control transmission scheduling and/or communicationresource allocation, e.g., the assignment of uplink and downlink segmentto WTs. Base station control routine 1836 also includes, in someembodiments, e.g., those including channel estimation boundary switchingmodule 1812 and multiple receive antennas (1806, 1808), a receiverantenna switching control module 1840. Base station control routines1836 also includes, in some embodiments, e.g., those including switchingmodule 1820 and multiple transmit antennas (1814, 1816), a transmitterantenna switching control module 1842. The switching devices 1812 inthis receiver chain 1810 and 1820 in the transmitter chain 1818, whenimplemented, are responsive to control signals generated by theprocessor 1826 when operating under direction of these modules (1840,1842), respectively. The control signals cause switching betweenantennas or antenna elements in accordance with the invention. Thereceiver antenna switching control modules 1840 may use thedata/information 1832 including the uplink quality indicator feedbackinformation 1858, received uplink signaling channel estimationinformation 1868, and receiver antenna switching information 1874 inmaking antenna switching decisions. The transmitter antenna switchingcontrol module 1842 may use the data/information 1832 including thereceived downlink channel feedback report information 1859, andtransmitter antenna switching information 1876 in making antennaswitching decisions.

Base station control routine 1836 also includes uplink channel feedbackmodule 1844 which controls the evaluation of received uplink signals,generation, and transmission of channel quality indicator feedbacksignals such as feedback messages 1864 including WT power controlfeedback information 1860 and transmission acknowledgment/negativeacknowledgement (ack/nak) feedback information 1862 indicating thesuccess or failure in receipt of an uplink signal or signals.

Memory 1828 also includes data/information 1832 used by communicationsroutines 1834 and control routine 1836. Data/information 1832 includesWT data/information 1846 and system information 1848. WTdata/information 1846 includes a plurality of sets of WT information (WT1 data/information 1850, WT N data/information 1852). WT 1data/information 1850 includes user/device/session/resource information1854, timing synchronization information 1856, uplink quality indicatorfeedback message information 1858, and received downlink channelfeedback report information 1859. User/device/session/resourceinformation 1854 includes user/device identification information,session information such as peer node information and routinginformation, and resource information such as uplink and downlinktraffic channel segments assigned by the scheduler 1838 to WT1. Timingsynchronization information 1856 includes information to synchronize WT1timing with respect to BS timing, e.g., adjustment information tocompensate for propagation delays. Uplink quality indicator feedbackmessage information 1858 includes WT power control information 1860,ack/nak information 1862, and feedback messages 1864. Received downlinkchannel feedback report information 1859 includes information obtainedfrom a received downlink channel feedback report transmitted by WT1 inresponse to downlink pilot broadcast signals transmitted by BS 1800.System information 1848 includes received uplink signaling channelestimation information 1868, CDMA information 1870, OFDM information1872, optionally receiver antenna switching information 1874, andoptionally transmitter antenna switching information 1876. Receiveduplink signaling channel estimation information 1868 includes aplurality of sets of channel estimation information (channel estimate 1information 1878, channel estimate N information 1880), each channelestimate corresponding to a channel estimate of received uplinksignaling from one WT using one antenna or antenna element. Informationfrom channel estimates 1878, 1880 is associated with specific WTs,processed, and stored, e.g., in WT power control info 1860 and ack/nakinfo 1862. Information 1868 also includes channel boundary information1882 and estimate reset information 1884. Channel boundary information1882 identifies the times defining where the BS switches betweenintervals associated with a plurality of different channel estimates forthe same WT, e.g., different channel estimates being associated withdifferent WT transmitter antenna elements. Estimate reset information1884 includes information identifying times that channel estimates arere-initialized, e.g., channel boundaries where a channel estimationfilter is cleared and restarted.

CDMA information 1870 includes carrier frequency information, bandwidthinformation, CDMA timing synchronization information, and codewordinformation. OFDM information 1872 includes OFDM timing information,dwell information including dwell boundary information, toneinformation, and tone hopping information. In some embodiments, BS 1800supports either CDMA communications or OFDM communications 1872, but notboth, in which case the BS 1800 includes CDMA info 1870 or OFDM info1872.

Receiver antenna switching information 1874 includes information such asswitching criteria, predetermined switching sequences, antenna elementutilization information, and antenna element control information used bythe receiver antenna switching control module 1840. Transmitter antennaswitching information 1876 includes information such as switchingcriteria, predetermined switching sequences, antenna element utilizationinformation, and antenna element control information used by thetransmitter antenna switching control module 1842.

FIG. 16 illustrates another exemplary base station—access node 1900,implemented in accordance with the present invention. BS 1900 may any ofthe exemplary BSs (12, 12′) of FIG. 13. The BS 1900 includes receiverchain/antenna module 1902 and a transmitter chain/antenna module 1904.The receiver chain/antenna module 1906 includes a receive antenna 1 1906and a receiver chain 1908. The receiver chain antenna module 1906receives uplink signals from different transmit antennas or antennaselements from the same WT, said signals including different subsets oftones, and said signals transmitted simultaneously from the same WT. Insome embodiments, e.g., with a controllable baseband transmitter unit1914, the BS 1900 includes a plurality of transmitter chain/antennas(1904, 1904′); module 1904 includes transmit chain 1 1912 coupled totransmit antenna or antenna element 1 1910, while module 1904′ includestransmit chain N 1912′ coupled to transmit antenna or antenna element N1910′. Using multiple transmitter chains/antenna modules 1904, 1904′with subsets of frequencies or tones being transmitted at the same timeon different antennas or antenna elements is used to obtain diversity,in accordance with the present invention. Transmitter chain/antennamodule 1 1904 includes a transmit antenna 1910 coupled to a transmitchain 1912. Similarly, transmitter chain/antenna module N 1904′ includesa transmit antenna 1910′ coupled to a transmitter chain 1912′. Thetransmitter chains 1912, 1912′ are coupled to the controllable basebandtransmitter unit 1914. Receiver module 1902, optionally controllablebaseband transmitter unit 1914, a processor 1916, e.g., CPU, I/Ointerface 1918, and a memory 1920 are coupled together via a bus 1922over which the various elements may interchange data and information. Insome embodiments without controllable baseband transmitter unit 1914,transmitter chain/antenna module 1904 is coupled to bus 1922. I/Ointerface 1918 couples the BS 1900 to the Internet and to other networknodes, e.g., other BSs 1900, AAA nodes, home agent nodes, routers, etc.Memory 1920 includes routines 1924 and data/information 1926.

Processor 1916, under control of one or more routines 1924 stored inmemory 1920, uses the data/information 1926 and causes the base station1900 to operate in accordance with the methods of the present invention.Routines 1924 include communications routine 1928 and base stationcontrol routine 1930. Communications routine 1928 performs variouscommunications protocols and functions used by BS 1900. The base stationcontrol routine 1930 is responsible for insuring that the base station1900 operates in accordance with the methods of the present invention.

The base station control routine 1930 includes a scheduler module 1932and an uplink channel feedback module 1936. In some embodiments, e.g.,some embodiments including controllable baseband transmitter unit 1914and transmitter chain/antenna module 1904′, base station control routine1930 also includes a frequency transmit splitting control module 1934.The scheduler module 1932, e.g., a scheduler, schedules air linkresources, e.g., uplink and downlink segments, to WTs.

The frequency transmit splitting control module 1934, when implemented,controls the operation of the controllable baseband transmitter unit1914 to split the frequencies, e.g., set of tones, used fortransmission, thus routing some of the information using a first subsetof tones to transmitter chain antenna module 1 1904 and some of theinformation using a second subset of tones, to transmitter chain/antennamodule N 1904′, the first and second subsets of tones being differentfrom one another by at least one tone. In some embodiments, more thantwo antennas or antenna elements are used for simultaneous transmissionand more than two subsets of tones are simultaneously transmitted, e.g.,one subset of tones corresponding to each antenna or antenna element tobe used simultaneously. In some embodiments, the different subsets oftones associated with different transmitter chains/antennas are mutuallyexclusive. In some embodiments, there is partial overlapping between thetone subsets. In accordance with the invention, BS 1900 cansimultaneously transmit both first and second sets of tones, the firstset of tones being convey by a first communications channel from antenna1 1910 to the WT, and the second set of tones being conveyed by a secondcommunications channel from antenna N 1910′ to the same WT. Thefrequency splitting control module 1934 includes an assignmentsub-module 1938 for assigning tones from a set of tones to a pluralityof different tone sub-sets including at least a first and a second tonesubset, each of said different tone subsets being different from oneanother by at least one tone. The frequency splitting control module1934 also includes a transmission sub-module for controlling thetransmission of the selected subsets of tones.

Assignment sub-module 1938 uses data/information 1926 includingpredetermined switching sequence information 1988, switching criteriainformation 1986, received downlink channel report feedback information1958, tone set info 1970, and/or hopping info 1972 to decide on andassign tones to the tone subsets (tone subset 1 info—interval 1 1974,tone subset N—interval 1 1976, tone subset 1 info—interval M 1978, tonesubset N info—interval M 1980). The assignment sub-module 1938 alsogenerates and stores antenna element control information (antennaelement 1 switching control information 1992, antenna element Nswitching control information 1994). Transmission sub-module 1940 usesthe data/information 1926 including the tone subsets (1974, 1976, 1978,1980), OFDM timing information 1948, and antenna element switchingcontrol information (1992, 1993) to implement the decisions of theassignment module and control the operation of the controllable basebandtransmitter unit 1914.

Uplink channel feedback module 1936 evaluates and processes receiveduplink signaling, obtaining WT power control information 1960 andACK/NAK information 1962. From the information 1960, 1962, the uplinkchannel feedback module 1936 generates feedback messages 1964, which aresubsequently transmitted to the WTs to be used in making decisions as totone splitting among WT transmission antennas or antenna elements.

Data/information 1926 includes WT data/information 1942, uplink toneinformation 1944, downlink OFDM tone information 1946, and OFDM timinginformation 1948. In some embodiments, e.g., embodiments includingfrequency transmit splitting control module 1934, data/information 1926also includes frequency splitting information 1950.

WT data/info 1942 includes a plurality of sets of data/information (WT1data/information 1951, WTN data/information 1952). WT 1 data/info 1951includes user/device/sessions/resource information 1953, timingsynchronization information 1954, uplink quality indicator feedbackmessage information 1956, and received downlink channel feedback reportinformation 1958. User/device/session/resource information 1953 includesuser/device identification information, session information includingpeer node identification and routing information, and resourceinformation including uplink and downlink segments assigned by the BS1900 to WT1.

Timing synchronization information 1954 includes information used tosynchronize WT1 with BS 1900, e.g., to account for delay propagation.

Uplink quality indicator feedback message information 1956 includes WTpower control information 1960, e.g., a received power level of a WT1uplink signal, an SNR value, a WT1 transmission power adjustment signal,etc. indicative of uplink channel quality, acknowledgment/negativeacknowledgement (ack/nak) signal information 1962, e.g., informationindicating the success or failure in receipt of a WT1 transmitted uplinksignal or signals, and feedback messages, e.g., messages to becommunicated to WT1 including information from 1960 and/or 1962.

Received downlink channel feedback report information 1958 includesinformation from WT feedback reports, e.g., reporting back on thequality of the downlink channel in terms of power levels, SNRs, etc.based on received pilot signals. Received downlink channel feedbackreport information also includes ack/nak signal information communicatedby the WT1 in response to downlink signals, e.g., downlink trafficchannel signals. Information 1958 is used, in some embodiments, by theassignment sub-module 1938 in the frequency splitting control module1934 when making decisions as to tone splitting.

Uplink tone information 1944 include tone set information 1944, e.g., aset of tones used for uplink signaling to the BS 1900 from WTs andhopping sequence information, e.g., an uplink hopping sequence used bythe WTs, the hopping changing between dwells.

Downlink OFDM tone information 1946 includes tone set information 1970,e.g., a set of tones used for downlink signaling by the BS, and hoppinginformation 1972, e.g., downlink hopping sequence which changes the tonemapping on an OFDM symbol time basis. OFDM tone information 1946 alsoincludes, in some embodiments, e.g., some embodiments with frequencytransmit splitting control module 1934, a plurality of tone subsets(tone subset 1 information—interval 1 1974, tone subset Ninformation—interval 1 1976, tone subset 1 information—interval M 1978,tone subset N information—interval M 1980). Each tone subset ofinformation (1974, 1976) being associated with a different transmitterchain/antenna (1904, 1904′), and the tone subsets (1974, 1976) to betransmitted simultaneously, in accordance with the invention. Similarly,each of the tone subsets of information (1978, 1980) is associated witha different transmitter chain/antenna (1904, 1904′), and the tonesubsets (1978, 1980) are be transmitted simultaneously, in accordancewith the invention. The weighting of tones, e.g., number of tonesassociated with each of the subsets, can change as a function of time.For example, during interval 1, tone subset 1 associated withtransmitter chain/antenna 1 may use 6 tones and tone subset 2 associatedwith transmitter chain/antenna 2 may use 6 tones; however during thenext successive interval, tone subset 1 associated with transmitterchain/antenna 1 may use 7 tones and tone subset 2 associated withtransmitter chain 2/antenna 2 may use 5 tones. In addition, from OFDMsymbol transmission time interval to OFDM symbol transmission timeinterval, the set of tones may be hopped according to a downlink tonehopping sequence.

OFDM timing information 1948 includes symbol timing information 1982 anddwell information 1984. Symbol timing information 1982 including thetiming defining the transmission of a single OFDM symbol includingmultiple tones transmitted simultaneously. Dwell information 1984includes information identifying a number of successive of OFDM symbols,e.g., 7, where the uplink tone mapping from logical to physical tonesdoes not change for the duration of the dwell; the tones being hoppeddifferently from dwell to dwell. Dwell information 1984 also includesinformation identifying dwell boundaries.

In some embodiments, the frequency splitting is on a predeterminedbasis, e.g., the tones being divided among the plurality of transmitterchain/antenna modules (1904, 1904′), e.g., in an alternating sequencewith respect to physical indexing numbers. In other embodiments,weighting between the different transmitter chain/antenna modules (1904,1904′) changes as a function of received downlink channel feedbackreport information 1958 and the switching criteria information 1986 inthe frequency splitting information 1950. For example, if the BS 1900includes a first and second transmitter chain/antenna module 1904 and1904′ and the feedback information indicates that the channel qualitiesare substantially equivalent, e.g., the difference in channel qualitiesis below a first criteria level, the tones may be split evenly betweenthe two modules 1904, 1904′. However, if the same exemplary BS 1900determines that the quality of the channel corresponding to transmitterchain/antenna module 1904 is significantly better than the channelquality corresponding to transmitter module 1904′, yet the channelquality of both channels is still acceptable, based on feedbackinformation and comparisons to second and third criteria levels, thenthe frequency splitting control module 1934 can control basebandtransmitter unit 1914 to dedicate more tones, e.g., twice as many tonesto module 1904 as to module 1904′.

Frequency splitting information 1950 includes switching criteriainformation 1986, predetermined switching sequence information 1988,antenna element utilization information 1990, and a plurality of sets ofantenna element switching control information (antenna element 1switching control information 1992, antenna element N switching controlinformation 1994). Switching criteria information 1986 includesthreshold limits used by the assignment sub-module 1938 in evaluatingthe antenna element feedback info included or derived from receiveddownlink channel feedback report info 1958 in making decisions as towhether, when, and to what extend to change the balance of tones splitbetween the various transmitter chains/antennas (1904, 1904′).Predetermined switching sequence information 1988 includes a pluralityof predetermined sequences that may be selected among by the assignmentsub-module 1938. For example, a first predetermined sequence mayalternate, e.g., on each or some fixed number of OFDM symboltransmission time interval or intervals, between (i) a 50-50 split ofuplink tones between a first transmitter chain/antenna and secondtransmitter chain/antenna and (ii) a 60-40 split of uplink tones betweenthe first transmitter chain/antenna and the second transmitterchain/antenna; a second predetermined sequence may alternate, e.g.,between (i) a 50-50 split of uplink tones between a first transmitterchain/antenna and second transmitter chain/antenna and (ii) a 40-60split of uplink tones between the first transmitter chain/antenna andthe second transmitter chain/antenna. In some embodiments, the BS 1900shall follow a predetermined switching sequence, which does not changeas a function of feedback information, e.g., a fixed predeterminedsequence which results in equal or nearly equal frequency splittingamong transmitter chains/antennas (1904, 1904′) over time. Antennaelement utilization information 1990 includes information identifyingthe utilization of each antenna element (1910, 1910′), e.g., in terms ofnumber of tones in the assigned tone subset relative to the set of tonesor relative to the other tone subsets to be simultaneously transmittedover different transmit antenna elements. Antenna element switchingcontrol information (antenna element 1 switching control information1992, antenna element N switching control information 1994) includesinformation such as number of tones, index or frequency of assignedtones associated with antenna element (1,N), respectively. Information1992, 1994 is used by the controllable baseband transmitter unit 1914.

FIG. 17 illustrates an exemplary wireless terminal (WT) 1500, e.g.,mobile node (MN), implemented in accordance with the present invention.Exemplary WT 1500 can switch between multiple transmit antennas orantenna elements on dwell boundaries, but not in between, in accordancewith the present invention. MN 1500 may be any of the exemplary MNs (14,16, 14′, 16′) of FIG. 13. Exemplary WT 1500 may be used in conjunctionwith exemplary BS 1400 of FIG. 14. The mobile node 1500 may be used as amobile terminal (MT). The mobile node 1500 includes receiverchain/antenna module 1502 and transmitter chain/antenna module 1504which may be implemented as shown in FIGS. 8 and 3, respectively. Asingle transmitter chain 1518 and transmit antenna switching is used toobtain diversity in accordance with the present invention. The receiverchain/antenna module 1502 includes receive antenna 1 1506 and a receivechain 1510. In some embodiments, receiver chain/antenna module 1502includes multiple antennas or multiple antenna elements (receive antenna1 1506, receive antenna N 1508), and receiver chain 1510 includes acontrollable switching module 1512, e.g. switching circuitry. Thetransmitter chain/antenna module 1504 includes multiple antennas ormultiple antenna elements (transmit antenna 1 1514, transmit antenna N1516) and a single transmitter chain 1518 including a controllable dwellboundary switching module 1520. In some embodiments, the plurality oftransmit antennas or antenna elements (1514, 1516) are oriented indifferent directions. In some embodiments, the plurality of differentantennas or antenna elements (1514, 1516) are spaced apart so that adifferent communications path exists between the antennas or antennaelements and the base station. In some embodiments, the spacing betweenantennas or antenna elements is at least ¼ of a wavelength of the lowestfrequency tone transmitted from the antenna or antenna element. Thereceiver module 1502, transmitter module 1504, a processor 1522, e.g.,CPU, user I/O devices 1524, and a memory 1526 are coupled together via abus 1528 over which the various elements may interchange data andinformation. Memory 1526 includes routines 1530 and data/information1532.

The receiver chain/antenna module 1502 receives downlink signals by basestations including feedback signals such as quality indicator signalsindicative of the quality of uplink signals. The transmitterchain/antenna module 1504 transmits uplink signals including uplinktraffic channel signals to a base station, using a plurality of transmitantennas or antenna elements (1514, 1516), in which one of the pluralityof antennas is coupled to the single transmitter chain 1518 for anygiven dwell, in accordance with the present invention.

Processor 1522 executes the routines 1530 and uses the data/information1532 in memory 1526 to control the operation of the WT 1500 andimplement the methods of the present invention. User I/O devices 1524,e.g., displays, speaker, microphone, keyboard, keypad, mouse, etc allowthe user of WT 1500 to input user data and information intended for apeer node and to output user data and information from a peer node.

Routines 1530 include communications routine 1534 and mobile nodecontrol routine 1536. The mobile node control routine 1536 includes atransmitter antenna switching control module 1538 and an uplink channelfeedback module 1540. In some embodiments, e.g., embodiments includingmultiple receiver antennas 1506, 1508 and switching module 1512, themobile node control routine 1536 includes a receiver antenna switchingcontrol module 1542.

Data/information 1532 includes user/device/resource information 1544,uplink channel condition feedback information obtained from a basestation 1546, and dwell information 1548. User/device/session/resourceinformation 1544 includes information pertaining to communicationssessions between WT1 500 and peer nodes such as, e.g., routinginformation, identification information, assigned traffic channelsegment information, etc.

Uplink channel condition feedback information from base station 1546includes received quality indicator signal information 1550 and aplurality of sets of antenna feedback information (antenna element 1feedback information 1556, antenna element N feedback information 1558).A base station receiving uplink signals from WT 1500 determines thequality of the received uplink signals and sends feedback signals to WT1500 indicative of the received quality. Received quality indicatorsignal information 1550 is information conveyed in those feedbacksignals and includes transmission power control signal information 1552and transmission acknowledgment signal information 1554. Transmissionpower control signal information 1552 can include information indicativeof power levels, relative power levels, signal-to-noise ratios, andcommanded power level changes. Transmission acknowledgement signalinformation 1554 can include information indicating success or failurein receipt of a transmitted uplink signal or signals, e.g., asrepresented by an ack/nak or statistical information on acks/naks.

The base station need not know, and in many embodiments does not knowthat the WT 1500 is switching between multiple transmit antennas and/orwhen the WT 1500 is switching. The WT 1500 can use its knowledge as towhich WT transmit antenna (1514, 1516) the WT 1500 used for a specificdwell and correlate the received feedback information, e.g., ack/naksreceived, with specific antennas, thus forming and maintaining sets offeedback information by antenna (antenna element 1 feedback information1556, antenna element N feedback information 1558). In some embodiments,where the base station has knowledge of the different transmit antennas(1514, 1516) being used by the WT 1500, the BS can maintain differentsets of feedback information and convey those sets to WT 1500 to bestored as antenna element feedback sets (antenna element 1 feedback info1556, antenna element N feedback info 1558), without the WT 1500 havingto perform the correlation.

Dwell information 1548 includes dwell characteristic information 1560and dwell switching information 1562. Dwell characteristic informationincludes a specified number of OFDM symbol transmission time periods perdwell 1564, e.g., seven, dwell boundary information 1566, toneinformation 1568 and tone hopping sequence information 1574. Dwellboundary information 1566 includes timing information used by WT 1500 todistinguish when one dwell ends and the next dwell begins, and dwellboundary information 1566 is used to control the switching betweentransmit antennas (1514, 1516) so that antenna switching is performed onat least some dwell boundaries but not in between. Tone information 1568includes dwell index N information 1570 and dwell index N+1 information1572. Dwell index N information 1570 includes a set of tones to be usedby the WT 1500 to transmit uplink signals to a base station during afirst dwell, while dwell N+1 information 1572 includes a set of tones tobe used by the WT 1500 to transmit uplink signals to the base stationduring a second dwell, the second dwell being an immediately consecutivedwell to the first dwell. The tone hopping sequence information 1574includes information defining the hopping sequence from logical tophysical tones to be used by WT 1500 in the uplink signaling, and thusis used in determining the dwell index N information 1570 and dwellindex N+1 information 1572.

Dwell switching information 1562 includes switching criteria information1576, predetermined switching sequence information 1578, antenna elementutilization information 1580, and a plurality of sets of antennaswitching control information (antenna element 1 switching controlinformation 1582, antenna element N switching control information 1584).Switching criteria information 1576 includes information identifyingmethods and limits used for determining dwell boundary switching betweentransmit antennas (1514, 1516). For example, switching criteriainformation 1576 may include threshold limits that are applied toreceived feedback quality levels to determine switching. For example,one criteria may be a ratio value of naks/acks corresponding to oneantenna that if exceeded triggers a transition to a different antennaelement or is used to trigger a different proportion of number of thenumber of dwells allocated to a first antenna with respect to the numberof dwells allocated to a second transmit antenna, in a given time orgiven number of dwells. Predetermined switching sequence information1578 includes information identifying predetermined dwell boundaryswitching sequences that may be used. For example, an exemplary sequencemay couple the single transmit chain 1518 to one of the antennas, e.g.,antenna 1514, for a fixed number of successive dwells, and then switchto another transmit antenna, e.g., antenna 1516, and remain there forthe same number of successive dwells, and then repeat the process,alternating between each of the transmit antennas (1514, 1516), andresulting in equal transmit antenna utilization. This method can beextended for more than two antennas, where the transmit antennautilization is equal among each antenna. In some embodiments, whenoperating on a fixed predetermined switching sequence, received qualityindicator signal information 1550 is not needed or used by the WT 1500,in performing dwell boundary switching, e.g., the WT 1500 follows apredetermined dwell boundary switching sequence irrespective of thevariations in channel quality between the different antenna (1514,1516). In other embodiments, predetermined switching sequences are usedin conjunction with uplink channel condition feedback information fromthe BS 1546. For example, different predetermined switching sequencesfrom information 1578 may be selected based on the quality feedbackinformation, e.g., a specific predetermined sequence which favors onetransmit antenna or rejects one transmit antenna. Alternately, in someembodiments, predetermined switching sequences are used initially and/orintermittently to evaluate different channel qualities, and then dwellboundary switching is based upon uplink channel quality feedbackinformation. In some embodiments, a predetermined switching sequence isnot used, and dwell boundary switching is performed as a function ofuplink channel quality. Antenna utilization information 1580 includesinformation identifying the current utilization of each of the transmitantennas (1514, 1516), e.g., in terms of time and/or number of dwells inrelation to the other transmit antennas, and changes in antennautilization to be performed.

Different sets of switching control information (antenna element 1switching control information 1582, antenna element N switching controlinformation 1584) are maintained by the WT 1500 corresponding to thedifferent sets of antenna feedback information (antenna element 1feedback information 1556, antenna element N feedback information 1558).

Data/information 1532, previously described, can be used, in someembodiments, to select one or more channels from a plurality of channelscreated in accordance with the invention, the selected one or morechannels having a higher channel quality than other channels, theselected one or more channels to be used more than the other channelswith lower channel quality.

Communications routine 1534 implements the various communicationsprotocols used by the WT 1500. The mobile node control routine 1536controls the WT functionality including operation of receiver module1502, transmitter module 1504, user I/O devices 1524, and implements themethods of the present invention including the processing of feedbackinformation indicative of uplink signaling and the implementation andcontrol of dwell boundary switching of the single transmitter chain 1518between different antennas or antenna elements (1514, 1516), inaccordance with the present invention.

Transmitter antenna switching control module 1538 uses thedata/information 1532 to implement the dwell boundary switching methodincluding making decisions regarding: antenna utilization, sequences,changes in sequences, and changes due to quality feedback information.For example, if the channel quality corresponding to antenna 1 1514 isdetermined by the WT 1500 to be higher than the channel qualitycorresponding to antenna N 1516, the transmitter antenna switchingcontrol module 1538 can, in some embodiments, select to use antenna 11514 for 3 dwells and antenna N 1516 for one dwell out of every foursuccessive dwells. The transmitter antenna switching control module 1538also controls the operation of the dwell boundary switching module 1520,e.g., via control select signals, to implement switching decisions.

Uplink channel feedback module 1540 controls the processing of receivedfeedback signals extracting transmission power control signalinformation 1552 and/or transmission acknowledgment signal information1554. Uplink channel feedback module 1540 can also separate the receivedfeedback information 1550, using its knowledge as it which dwell wasassociated with which WT transmit antenna, into sets of informationassociated with different antennas (antenna element 1 feedbackinformation 1556, antenna element N feedback information 1558). Theoutput information obtained from the uplink channel feedback module 1540can be used as input by the transmitter antenna switching control module1538 to be used in reaching dwell switching decisions.

The optional receiver antenna switching control module 1542, whenimplemented, is used to control the switching of the receive chainswitching control module 1512 to connect, at any one time, one of theplurality of receive antennas or antenna elements (1506, 1508) to thesingle receive chain 1510. Receiver antenna switching control module1542 sends a control select signal to switching module 1512 to controlthe antenna selection. The receiver antenna switching control module1542, by switching between antennas 1506, 1508 can provide receivediversity. Various implementations are possible in regard to theswitching decision methodology, e.g., periodic switching betweenantennas (1506, 1508) and/or switching based on the quality of thereceived downlink signal, e.g., testing each channel and locking in onthe antenna resulting in the best quality downlink channel.

FIG. 18 illustrates another exemplary wireless terminal (WT) 1600, e.g.,mobile node (MN), implemented in accordance with the present invention.Exemplary WT 1600 can switch between multiple transmit antennas orantenna elements on signal boundaries corresponding to base stationchannel estimation signal boundaries, but not in between, in accordancewith the present invention. MN 1600 may be any of the exemplary MNs (14,16, 14′, 16′) of FIG. 13. Exemplary WT 1600 may be used in conjunctionwith exemplary BS 1800 of FIG. 15. The mobile node 1600 may be used as amobile terminal (MT). The mobile node 1600 includes receiverchain/antenna module 1602 and transmitter chain/antenna module 1604.Receiver/antenna module 1802 may be implemented similarly or the same asthat shown in FIG. 8. The transmitter/antenna module 1804 may beimplemented similarly to that shown in FIG. 3, but with the switchingcontrolled as a function of channel estimation boundary informationand/or uplink channel estimation feedback information. A singletransmitter chain 1618 and transmit antenna switching is used to obtaindiversity, in accordance with the present invention. The receiverchain/antenna module 1602 includes receive antenna 1 1606 and a receivechain 1610. In some embodiments, receiver chain/antenna module 1602includes multiple antennas or multiple antenna elements (receive antenna1 1606, . . . , receive antenna N 1608), and receiver chain 1610includes a controllable switching module 1612, e.g. switching circuitry.The transmitter chain/antenna module 1604 includes multiple antennas ormultiple antenna elements (transmit antenna 1 1614, . . . , transmitantenna N 1616) and a single transmitter chain 1618 including acontrollable channel estimation boundary switching module 1620. In someembodiments, the plurality of transmit antennas or antenna elements(1614, 1616) are oriented in different directions. In some embodiments,the plurality of different antennas or antenna elements (1614, 1616) arespaced apart so that a different communications path exists between theantennas or antenna elements and the base station. In some embodiments,the spacing between antennas or antenna elements is at least ¼ of awavelength of the lowest frequency tone transmitted from the antenna orantenna element. The receiver module 1602, transmitter module 1604, aprocessor 1622, e.g., CPU, user I/O devices 1624, and a memory 1626 arecoupled together via a bus 1628 over which the various elements mayinterchange data and information. Memory 1626 includes routines 1630 anddata/information 1632.

The receiver chain/antenna module 1602 receives downlink signals by basestations including feedback signals such as quality indicator signalsindicative of the quality of uplink signals. The transmitterchain/antenna module 1604 transmits uplink signals including uplinktraffic channel signals to a base station, using a plurality of transmitantennas or antenna elements (1614, 1616), in which one of the pluralityof antennas is coupled to the single transmitter chain 1618 at any giventime, in accordance with the present invention.

Processor 1622 executes the routines 1630 and uses the data/information1632 in memory 1626 to control the operation of the WT 1600 andimplement the methods of the present invention. User I/O devices 1624,e.g., displays, speaker, microphone, keyboard, keypad, mouse, etc allowthe user of WT 1600 to input user data and information intended for apeer node and to output user data and information from a peer node.

Routines 1630 include communications routine 1634 and mobile nodecontrol routine 1636. The mobile node control routine 1636 includes atransmitter antenna switching control module 1638 and an uplink channelfeedback module 1640. In some embodiments, e.g., embodiments includingmultiple receiver antennas 1606, 1608 and switching module 1612, themobile node control routine 1636 also includes a receiver antennaswitching control module 1642.

Data/information 1632 includes user/device/session/resource information1644, uplink channel condition feedback information obtained from a basestation 1646, channel estimation interval information 1648 and channelestimation boundary switching information 1650.User/device/session/resource information 1644 includes informationpertaining to communications sessions between WT 1600 and peer nodessuch as, e.g., routing information, identification information, assignedtraffic channel segment information, etc.

Uplink channel condition feedback information from base station 1646includes received quality indicator signal information 1652 and aplurality of sets of antenna feedback information (antenna element 1feedback information 1658, antenna element N feedback information 1660).A base station receiving uplink signals from WT 1600 determines thequality of the received uplink signals and sends feedback signals to WTindicative of the received quality. Received quality indicator signalinformation 1652 is information conveyed in those feedback signals andincludes transmission power control signal information 1654 andtransmission acknowledgment signal information 1656. Transmission powercontrol signal information 1654 can include information indicative ofpower levels, relative power levels, signal-to-noise ratios, andcommanded power level changes. Transmission acknowledgement signalinformation 1656 can include information indicating success or failurein receipt of a transmitted uplink signal or signals, e.g., asrepresented by an ack/nak or statistical information on acks/naks.

The base station need not know, and in many embodiments does not knowthat the WT 1600 is switching between multiple transmit antennas and/orwhen the WT 1600 is switching. However, the WT 1600 tracks the channelestimation intervals being used by the base station, and when switchingbetween transmit antenna occurs, it occurs on a channel estimationboundary. For example, the base station can perform 1 channel estimationin a fixed amount of time, and then reinitialize the channel estimationand restart; the WT 1600 can select the time corresponding to there-initialization point to switch antennas. The WT 1600 can use itsknowledge as to which WT transmit antenna (1614, 1616) the WT 1600 usedfor the interval corresponding to the channel estimation and correlatethe received feedback information, e.g., ack/naks received, withspecific antennas, thus forming and maintaining sets of feedbackinformation by antenna (antenna element 1 feedback information 1658,antenna element N feedback information 1660). In some embodiments, thebase station maintains different ongoing channel quality estimates, e.g.one corresponding to each transmit antenna (1614, 1616), and the basestation alternates between these ongoing channel estimates incoordination with the WT transmit antenna switching. This implementationis useful where the WT 1600 operates with a fixed number of transmitantennas (1614, 1616) on a predetermined periodic sequence, e.g., withuniform utilization between each antenna. In some embodiments, where thebase station has knowledge of the different transmit antennas (1614,1616) being used by the WT 1600, the BS can maintain different sets offeedback information and convey those sets to WT 1600 to be stored asantenna element feedback sets (antenna element 1 feedback info 1658,antenna element N feedback info 1660), without the WT 1600 having toperform the correlation.

Channel estimation interval information 1648 includes timing informationcorresponding to base station channel estimation boundaries 1662 andsignal type information 1664. Timing information 1662 relates the basestation uplink signal channel estimation cycles and intervals withrespect to the WT timing so that antenna switching may be controlled attimes corresponding to channel estimation boundaries to help to preventcorruption of base station channel estimates by the mixture of uplinksignals from two different transmit antennas (1614, 1616). Signal typeinformation includes type selection 1666, code division multiple access(CDMA) information 1668, and orthogonal frequency division multiplexing(OFDM) information 1670. The type selection 1666 includes a user orservice provider selection of the type of communications signaling to beemployed between the WT 1600 to the base station, e.g., CDMA signalingor OFDM signaling. As a function of the selection different circuitry isactivated within WT 1600. CDMA information 1668 includes carrierfrequency used, bandwidth, codeword used, and channel estimationinterval time. OFDM information 1670 can include information identifyingdwell intervals defined by a number of successive OFDM symboltransmission time periods, information identifying dwell boundaries,tone information including the tones used in a given dwell, and tonehopping sequence information. In some embodiments, WT 1600 supports onetype of signaling but not the other, in which case, WT 1600 wouldinclude one set of information 1668 or 1670.

Channel estimation boundary switching information 1650 includesswitching criteria information 1672, predetermined switching sequenceinformation 1674, antenna element utilization information 1676, and aplurality of sets of antenna switching control information (antennaelement 1 switching control information 1678, antenna element Nswitching control information 1680). Switching criteria information 1672includes information identifying methods and limits used for determiningchannel boundary switching between transmit antennas (1614, 1616). Forexample, switching criteria information 1672 may include thresholdlimits that are applied to received feedback quality levels to determineswitching. For example, one criteria may be a minimum value of filteredSNR that if crossed triggers a transition to a different antennaelement. Predetermined switching sequence information 1674 includesinformation identifying predetermined channel estimation boundaryswitching sequences that may be used. For example, an exemplary sequencemay couple the single transmit chain 1618 to one of the antennas, e.g.,antenna 1614, for a fixed number of successive channel estimates, andthen switch to another transmit antenna, e.g., antenna 1616, and remainsthere for the same number of successive channel estimates, and thenrepeat the process, alternating between each of the transmit antennas(1614, 1616), and resulting in equal transmit antenna utilization. Thismethod can be extended for more than two antennas, where the transmitantenna utilization is equal among each antenna. In some embodiments,when operating on a fixed predetermined switching sequence, receivedquality indicator signal information 1652 is not needed or used by theWT 1600, in performing channel estimation boundary switching, e.g., theWT 1600 follows a predetermined channel estimation boundary switchingsequence irrespective of the variations in channel quality between thedifferent antenna (1614, 1616); however, WT 1600 needs to maintaintiming synchronization between the channel estimations performed by thebase station on the uplink signaling, and the switching points. In otherembodiments, predetermined switching sequences are used in conjunctionwith uplink channel condition feedback information from the BS 1646. Forexample, different predetermined switching sequences from information1674 may be selected based on the quality feedback information, e.g., aspecific predetermined sequence which favors one transmit antenna orrejects one transmit antenna. Alternately, in some embodiments,predetermined switching sequences are used initially and/orintermittently to evaluate different channel qualities, and then channelboundary switching is based upon uplink channel quality feedbackinformation. In some embodiments, a predetermined switching sequence isnot used, and channel boundary switching is performed as a function ofuplink channel quality. Antenna utilization information 1676 includesinformation identifying the current utilization of each of the transmitantennas (1614, 1616), e.g., in terms of time or duty cycle in relationto the other transmit antennas, and changes in antenna utilization to beperformed.

Different sets of switching control information (antenna element 1switching control information 1678, antenna element N switching controlinformation 1680) are maintained by the WT 1600 corresponding to thedifferent sets of antenna feedback information (antenna element 1feedback information 1658, antenna element N feedback information 1680).

Communication routine 1634 implements the various communicationsprotocols used by the WT 1600. The mobile node control routine 1636controls the WT functionality including operation of receiver module1602, transmitter module 1604, user I/O devices 1624, and implements themethods of the present invention including the processing of feedbackinformation indicative of uplink signaling and the implementation andcontrol of channel estimation boundary switching of the singletransmitter chain 1618 between different antennas or antenna elements(1614, 1616), in accordance with the present invention.

Transmitter antenna switching control module 1638 uses thedata/information 1632 to implement the channel estimation boundaryswitching method including making decisions regarding: antennautilization, sequences, changes in sequences, and changes due to qualityfeedback information. The transmitter antenna switching control module1638 controls the operation of the channel estimation boundary switchingmodule 1618, e.g., via control select signals, to implement switchingdecisions. Uplink channel feedback module 1640 controls the processingof received feedback signals extracting transmission power controlsignal information 1654 and/or transmission acknowledgment signalinformation 1656. Uplink channel feedback module 1640 can also separatethe received feedback information 1652, using its knowledge as it whichchannel estimation was associated with which WT transmit antenna, intosets of information associated with different antennas (antenna element1 feedback information 1658, antenna element N feedback information1660). In some embodiments, the base station communicates differentchannel estimation reports to WT 1600 for each of the antennas (1614,1616), and the uplink channel feedback module can store such informationin the appropriate feedback info set (1658, 1660). The outputinformation obtained from the uplink channel feedback module 1640 can beused as input by the transmitter antenna switching control module 1638to be used in reaching channel estimation boundary switching decisions.

The optional receiver antenna switching control module 1642, whenimplemented, is used to control the switching of the receive chainswitching control module 1612 to connect, at any one time, one of theplurality of receive antennas or antenna elements (1606, 1608) to thesingle receive chain 1610. Receiver antenna switching control module1642 sends a control select signal to switching module 1612 to controlthe antenna selection. The receiver antenna switching control module1642, by switching between antennas (1606, 1608) can provide receivediversity. Various implementations are possible in regard to theswitching decision methodology, e.g., periodic switching betweenantennas (1606, 1608) and/or switching based on the quality of thereceived downlink signal, e.g., testing each channel and locking in onthe antenna resulting in the best quality downlink channel.

FIG. 19 illustrates another exemplary wireless terminal (WT) 1700, e.g.,mobile node (MN), implemented in accordance with the present invention.MN 1700 may be any of the exemplary MNs (14, 16, 14′, 16′) of FIG. 13.Exemplary WT 1700 may be used in conjunction with exemplary BS 1900 ofFIG. 16. The mobile node 1700 may be used as a mobile terminal (MT). Themobile node 1700 includes receiver chain/antenna module 1702 and aplurality of transmitter chain/antenna modules (1704, 1704′) with acontrollable baseband transmitter unit 1718. The receiver chain/antennamodule 1702 may be implemented similarly to or the same as that shown inFIG. 8. The plurality of transmitter chain/antenna modules (1704, 1704′)with controllable baseband transmitter unit 1718 may be implemented thesame as or similarly to any of the embodiments shown in FIG. 27, 28, or29. The receiver chain/antenna module 1702 includes a receive antenna 11706 and a receiver chain 1710. In some embodiments receiver module 1702includes multiple receive antennas or antenna elements (receive antenna1 1706, receive antenna N 1708) and a controllable switching module1712, e.g. switching circuitry. Using multiple transmitterchains/antenna modules 1704, 1704′ with different set of frequencies ortones being transmitted at the same time on different antennas orantenna elements is used to obtain diversity, in accordance with thepresent invention. Transmitter chain/antenna module 1 1704 includes atransmit antenna 1714 coupled to a transmit chain 1716. Similarly,transmitter chain/antenna module N 1704′ includes a transmit antenna1714′ coupled to a transmitter chain 1716′. The transmitter chains 1716,1716′ are coupled to the controllable baseband transmitter unit 1718.Receiver module 1702, controllable baseband transmitter unit 1718, aprocessor 1720, e.g., CPU, user I/O devices 1722, and a memory 1724 arecoupled together via a bus 1726 over which the various elements mayinterchange data and information. User I/O devices 1722, e.g., keypads,keyboard, mouse, video camera, microphone, display, speaker, etc., allowthe user of WT 1700 to input user data/information to peer nodes andoutput user data/information from peer nodes. Memory 1724 includesroutines 1728 and data/information 1730.

Processor 1720, under control of one or more routines 1728 stored inmemory 1724 causes the mobile node 1700 to operate in accordance withthe methods of the present invention. Routines 1728 includecommunications routine 1732 and mobile node control routine 1734.Communications routine 1732 performs the various communicationsprotocols and functions used by WT 1700. The mobile node control routine1734 is responsible for insuring that the mobile node 1700 operates inaccordance with the methods of the present invention.

The mobile node control routine 1734 includes a frequency transmitsplitting control module 1736 and an uplink channel feedback module1738. In some embodiments, e.g., embodiments including receivercontrollable switching module 1712 and multiple receive antennas (1706,1708), control routine 1734 includes a receiver antenna switchingcontrol module 1740. In such embodiments, receiver antenna switchingcontrol may be performed under direction of receiver antenna switchingcontrol module 1740 which, when executed by the processor 1720, isresponsible for the generation of antenna switching control signal usedto control switching performed by the switching circuits in modules 1712in the receiver chain 1710.

The frequency transmit splitting control module 1736 controls theoperation of the controllable baseband transmitter unit 1718 to splitthe frequencies, e.g., set of tones, used for transmission, thus routingsome of the information using a first subset of tones to transmitterchain antenna module 1 1704 and some of the information using a secondsubset of tones, to transmitter chain/antenna module N 1704′, the firstand second subsets of tones being different from one another by at leastone tone. In some embodiments, more than two antennas or antennaelements are used for simultaneous transmission and more than twosubsets of tones are simultaneously transmitted, e.g., one subset oftones corresponding to each antenna or antenna element to be usedsimultaneously. In some embodiments, the different subsets of tonesassociated with different transmitter chains/antennas are mutuallyexclusive. In some embodiments, there is partial overlapping between thetone subsets. In accordance with the invention, WT 1700 cansimultaneously transmit both first and second sets of tones, the firstset of tones being convey by a first communications channel from antenna1 1714 to the BS, and the second set of tones being conveyed by a secondcommunications channel from antenna N 1714′ to the same base station.The frequency splitting control module 1736 includes an assignmentsub-module 1742 for assigning tones from a set of tones to a pluralityof different tone sub-sets including at least a first and a second tonesubset, each of said different tone subsets being different from oneanother by at least one tone. The frequency splitting control module1736 also includes a transmission sub-module for controlling thetransmission of the selected subsets of tones.

Assignment sub-module 1742 uses data/information 1730 includingpredetermined switching sequence information 1780, switching criteriainformation 1778, antenna element 1 feedback info 1758, antenna elementN feedback info 1760, tone set info 1762, and/or hopping info 1764 todecide on and assign tones to the tone subsets (tone subset 1info—interval 1 1766, tone subset N info—interval 1 1770, tone subset 1info—interval M 1768, tone subset N info—interval M 1772). Theassignment sub-module 1742 also generates and stores antenna elementcontrol information (antenna element 1 switching control information1784, antenna element N switching control information 1786).Transmission sub-module 1744 uses the data/information 1730 includingthe tone subsets (1766, 1770, 1768, 1772), OFDM timing information 1752,and antenna element switching control information (1784, 1786) toimplement the decisions of the assignment sub-module 1742 and controlthe operation of the controllable baseband transmitter unit 1718.

Uplink channel feedback module 1738 processes uplink channel qualityfeedback signals from the BS obtaining uplink channel condition feedbackinformation from BS 1748 including transmission power control signalinformation 1762 and transmission acknowledgement signal information1764. In many embodiments, the BS need not and does not know the tonesubset information corresponding to particular WT transmit antennachains/antennas (1704, 1704′) used; however, the WT 1700 knowing thetone subset information (1766, 1770, 1768, 1772), e.g., weighting interms of numbers of tones allocated to each antenna or antenna elementduring a specific dwell, correlates the feedback information 1756 tospecific antenna elements and stores the information as antenna element1 feedback information 1758, antenna element N feedback information1760.

Data/information 1730 includes user/device/session/resource information1746, uplink channel condition feedback information from the BS 1748,OFDM tone information 1750, OFDM timing information 1752, and frequencysplitting information 1754. User/device/session/resource information1746 includes user/device identification information, sessioninformation including peer node identification and routing information,and resource information including uplink and downlink segments assignedby the BS to WT 1700.

Uplink channel condition feedback information from BS 1748 includesreceived quality indicator signal information 1762 and a plurality ofset of antenna element feedback information (antenna element 1 feedbackinformation 1758), antenna element N feedback information 1760). Thereceived quality indicator signal information 1756 includes transmissionpower control signal information 1762, e.g., a received power level of aWT uplink signal, an SNR value, a WT transmission power adjustmentsignal, etc. indicative of channel quality, and transmissionacknowledgment signal information 1764, e.g., information from areceived transmission acknowledgement signal indicating the success orfailure in receipt of a WT transmitted uplink signal or signals. Antennaelement 1 feedback information 1758 and antenna element N feedbackinformation 1760 includes information which has been extracted and/orprocessed from the received quality indicator signal information1762,1764 by WT 1700 to be associated with each of the transmitterchains/antennas (1704, 1704′) used by the WT 1700.

OFDM tone information 1750 includes tone set information 1762, e.g., aset of tones used for uplink signaling by the WT, and hoppinginformation 1764, e.g., uplink hopping sequence information includinginformation defining a hopping sequence based on dwells which hopslogical tones to physical tones. OFDM tone information 1750 alsoincludes a plurality of tone subsets (tone subset 1 information—interval1 1766, tone subset N information—interval 1 1770, tone subset 1information—interval M 1768, tone subset N information—interval M 1772).Each tone subset of information (1766, 1770) being associated with adifferent transmitter chain/antenna (1704, 1704′), and the tone subsets(1766, 1770) are to be transmitted simultaneously, in accordance withthe invention. Similarly, each of the tone subsets of information (1768,1772) is associated with a different transmitter chain/antenna (1704,1704′), and the tone subsets (1768, 1772) are to be transmittedsimultaneously, in accordance with the invention. The weighting oftones, e.g., number of tones associated with each of the subsets, canchange as a function of time. For example, during interval 1, tonesubset 1 associated with transmitter chain/antenna 1 may use 6 tones andtone subset 2 associated with transmitter chain/antenna 2 may use 6tones; however during the next successive interval, tone subset 1associated with transmitter chain/antenna 1 may use 7 tones and tonesubset 2 associated with transmitter chain 2/antenna 2 may use 5 tones.In addition, from dwell to dwell the set of tone may be hopped accordingto an uplink tone hopping sequence.

OFDM timing information 1752 includes symbol timing information 1774 anddwell information 1776. Symbol timing information including the timingdefining the transmission of a single OFDM symbol conveying modulationsymbols conveyed on each of the tones transmitted. Dwell information1776 includes information identifying a number of successive of OFDMsymbols, e.g., 7, where the uplink tone mapping from logical to physicaltones does not change during the dwell; the tones being hoppeddifferently from dwell to dwell. Dwell information 1752 also includesinformation identifying dwell boundaries. In accordance with someembodiments of the invention, changes in weighting to subsets areperformed on dwell boundaries but not in-between.

In some embodiments, the frequency splitting is on a predeterminedbasis, e.g., the tones being divided among the plurality of transmitterchain/antenna modules (1704, 1704′), e.g., in an alternating sequencewith respect to physical indexing numbers. In other embodiments,weighting between the different transmitter chain/antenna modules (1704,1704′) changes as a function of uplink channel condition feedbackinformation 1748 and the switching criteria information 1778 in thefrequency splitting criteria information 1754. For example, if the WT1700 includes a first and second transmitter chain/antenna module 1704and 1704′ and the feedback information indicates that the channelqualities are substantially equivalent, e.g., the difference in channelqualities is below a first criteria level, the tones may be split evenlybetween the two modules 1704, 1704′. However, if the same exemplary WTdetermines that the quality of the channel corresponding to transmitterchain/antenna module 1704 is significantly better than the channelquality corresponding to transmitter module 1704′, yet the channelquality of both channels is still acceptable, based on feedbackinformation and comparisons to second and third criteria levels, thenthe frequency splitting control module 1736 can control basebandtransmitter unit 1718 to dedicate more tones, e.g., twice as many tonesto module 1704 as to module 1704′.

Frequency splitting information 1754 includes switching criteriainformation 1778, predetermined switching sequence information 1780,antenna element utilization information 1782, and a plurality of sets ofantenna element switching control information (antenna element 1switching control information 1784, antenna element N switching controlinformation 1786). Switching criteria information 1778 includesthreshold limits used by the assignment sub-module 1742 in evaluatingthe antenna element feedback info (1758, 1760) in making decisions as towhether, when, and to what extend to change the balance of tones splitbetween the various transmitter chains/antennas (1704, 1704′).Predetermined switching sequence information 1780 includes a pluralityof predetermined sequences that may be selected among by the assignmentmodule. For example, a first predetermined sequence may alternate, e.g.,on dwells, between (i) a 50-50 split of uplink tones between a firsttransmitter chain/antenna and second transmitter chain/antenna and (ii)a 60-40 split of uplink tones between the first transmitterchain/antenna and the second transmitter chain/antenna; a secondpredetermined sequence may alternate, e.g., on dwells, between (i) a50-50 split of uplink tones between a first transmitter chain/antennaand second transmitter chain/antenna and (ii) a 40-60 split of uplinktones between the first transmitter chain/antenna and the secondtransmitter chain/antenna. In some embodiments, the WT shall follow apredetermined switching sequence, which does not change as a function offeedback information, e.g., a fixed predetermined sequence which resultsin equal or nearly equal frequency splitting among transmitterchains/antennas (1704, 1704′) over time.

FIG. 21 is a flowchart 2100 of an exemplary method of operating a WT tocommunicate with a base station including performing dwell boundaryswitching of transmitter antenna elements, in accordance with thepresent invention. The WT may be, e.g., an exemplary WT similar to orthe same as WT 1500 of FIG. 17, and the BS may be, e.g., an exemplary BSsimilar to or the same as BS 1400 of FIG. 14. Operation starts in step2102 and proceeds to step 2104. In step 2104, a dwell boundary switchingmodule within the WT transmitter signal processing chain is operated tocouple a first antenna element from a set of multiple antenna elements,e.g., a set of two antenna elements, to a single transmitter chain.Operation proceeds from step 2104 to step 2106. In step 2106, the WT isoperated to transmit uplink signals to a base station through the firstantenna element during a first dwell using a set of tones fortransmission, the set of tones used for transmission matching a firstset of tones. The first dwell is a set of consecutive OFDM symboltransmission time intervals, e.g., a set of 7 consecutive OFDM symboltransmission time intervals during which the tone assignments fromlogical tone designation to physical tone designation do not change.

Next, in step 2108, the dwell boundary switching module is operated toswitch antenna elements from the first antenna element to the secondantenna element. Operation proceeds from step 2108 to step 2110. In step2110, the WT is operated to change the set of tones used fortransmission from the first set of tones to a second set of tonesaccording to an uplink tone hopping sequence, the second set of tonesbeing different than the first set of tones. Next, in step 2112, the WTis operated to transmit uplink signals to the base station through thesecond antenna element during a second dwell using the second set oftones. Operation proceeds from step 2112 to step 2114, in which the WTis operated to replace the tones in the first and second sets of tonesaccording to the uplink tone hopping sequence 2114. Operation proceedsfrom step 2114 to step 2104.

The operations of flowchart 2100 result in a predetermined and periodicswitching sequence between first and second antenna elements. Assumingthat the exemplary WT has only two transmitter antenna elements, theoperations of flowchart 2100 result in uniform utilization of antennaelements. In some embodiments, each of the antenna elements are orientedin a different direction. In some embodiments, the first and secondantenna elements are spaced apart so that a different communicationspath exists between each of the first and second antenna elements andthe base station. In some embodiments, the spacing between antennaelements is a t least ¼ of a wavelength of the lowest frequency tonetransmitted from the antenna element.

The methods of flowchart 2100 can be extended to include embodimentswith more than two antenna elements. In addition in some embodiments,the antenna may remain coupled to a selected antenna element for morethan one consecutive dwell, e.g., a fixed number of dwells greater than1, before switching to a different antenna element.

FIG. 22 is a flowchart 2200 of an exemplary method of operating a WT tocommunicate with a base station including performing dwell boundaryswitching of transmitter antenna elements, in accordance with thepresent invention. The WT may be, e.g., an exemplary WT similar to orthe same as WT 1500 of FIG. 17, and the BS may be, e.g., an exemplary BSsimilar to or the same as BS 1400 of FIG. 14. Operation starts in step2202 and proceeds to step 2204, where a dwell boundary switching modulewithin the WT transmitter signal processing chain is operated to couplethe single transmitter chain of the WT to a designated antenna elementform a set of multiple antenna elements, e.g., two transmit antennaelements. Then, in step 2206, the WT is operated to transmit uplinksignals to a base station through the designated antenna element duringa first dwell using a set of tones for transmission, the set of tonesused for transmission matching a first set of tones. The first dwell is,e.g., a set of seven consecutive OFDM symbol transmission timeintervals. Operation proceeds from step 2206 to step 2208. In step 2208,the WT is operated to receive a feedback signal or signals from the basestation, the feedback signal or signals indicative of channel quality ofthe received uplink signals from the previous dwell. The feedback signalor signals that are indicative of channel quality include at least oneof a transmission power control signal indicating WT uplink powercontrol information and a transmission acknowledgement signal indicatingsuccess or failure in receipt of a transmitted uplink signal or signals.Operation proceeds from step 2208 to step 2210. In step 2210, the WT isoperated to correlate received feedback signals or signals to theantenna element that was used during the previous dwell and update a setof feedback information corresponding to that antenna element. The basestation, which sent the feedback information, need not, and in manyembodiments, does not know which antenna element was used fortransmission of that dwell, the WT performing the tracking and matchingof antenna elements used with received feedback information. In step2212, the WT is operated to make an antenna element switching decisionas a function of received feedback signals. For example, if the powercontrol feedback signal indicates that the WT transmission power levelshould remain constant or be reduced and the ack/nak signals indicate avery high ratio of acks to naks, indicating a strong and reliable uplinksignal, the WT can be allowed to remain coupled to the currentlyselected transmitter antenna element. However, if the power controlfeedback signal indicates that a large increase in WT transmission poweris required and/or the ack/nak signals indicate a very high ratio ofnaks to acks, then the WT can decide to switch to another antennaelement, e.g., selecting an antenna element expected to produce a largechannel variation, e.g., an antenna element with the greatest spacingand/or largest orientation difference with respect to the currentlyselected antenna element. Stored information on the quality of channelswith previous WT transmission antenna element connections can also beused in the selection process. In a case, where the quality indicatorinformation indicates a marginal condition, the WT can be operated toselect an antenna element with a slight difference in spacing ororientation with respect to the currently selected antenna element.

Operation proceeds from step 2212 to step 2214. In step 2214, operationproceeds based upon whether or not the WT has decided to switch antennaelements. If the WT has decided in step 2212 not to switch antennaelements, then operation proceeds from step 2214, to step 2220;otherwise operation proceeds to step 2216. In step 2216, the WT isoperated to update and maintain switching control information setscorresponding to different antenna elements, e.g., operations includingsetting a bit corresponding to the antenna element to be connected tothe single transmitter chain and clearing a bit corresponding to theantenna element to be disconnected from the single transmitter chain.Operation proceeds from step 2216 to step 2218, in which the dwellboundary switching module is operated to switch the designated antennaelement to a different transmit antenna element form the set of multipleantenna elements, the different antenna element being the antennaelement selected in step 2212 and configured with control activationinformation in step 2216. In accordance with the invention, switching iscontrolled to be performed at dwell boundaries, but not in-between.Operation proceeds form step 2218 to step 2220.

In step 2220, the WT is operated to change the set of tones used fortransmission to a different set of tones in accordance with an uplinkhopping sequence. Then in step 2222, the WT is operated to transmituplink signals to the base station through the designated antennaelement during the next consecutive dwell, e.g., 7 consecutive OFDMsymbol transmission intervals, using the designated set of tones fortransmission from step 2220. Operation proceeds from step 2222 back tostep 2208.

The operations of flowchart 2200 result in dwell switching between aplurality of antenna elements based upon uplink channel quality feedbackinformation. In some embodiments, each of the antenna elements areoriented in a different direction. In some embodiments, the antennaelements are spaced apart so that a different communications path existsbetween each antenna elements and the base station. In some embodiments,the spacing between antenna elements is at least ¼ of a wavelength ofthe lowest frequency tone transmitted from the antenna element.

The methods of flowchart 2200 include embodiments with only two antennaelements and embodiments with more than two antenna elements. Inaddition in some embodiments, the antenna may remain coupled to aselected antenna element for more than one consecutive dwell, e.g., afixed number of dwells greater than 1, before a switching decision isperformed as to whether to switch to another antenna element. In someembodiments, feedback information is communicated more frequently orless frequently than once per dwell.

FIG. 23 is a flowchart 2300 of an exemplary method of operating a WT tocommunicate with a base station including performing channel estimationboundary switching of transmitter antenna elements, in accordance withthe present invention. The WT may be, e.g., an exemplary WT similar toor the same as WT 1600 of FIG. 18, and the base station may be, e.g., anexemplary BS similar to or the same as BS 1800 of FIG. 15. Operationstarts in step 2302 and proceeds to step 2304. In 2304, the WT isoperated to associate different base station uplink signaling channelestimates with different WT transmitter antenna elements. For example,based on some received downlink broadcast signals from the base station,the WT obtains information used to determine the timing of the basestation with regard to its channel estimations of received uplinksignaling, e.g., information defining boundaries between a plurality ofchannel estimates being performed and/or information defining boundariesdefining initialization or resets of channel estimates. For example, ifthe base station alternates periodically between two channel estimatesof uplink signaling, and the WT has two transmit antenna elements, thewireless terminal may associate a first channel estimate with a firstantenna element and a second channel estimate with a second antennaelement, and synchronize its uplink signaling timing such to correspondto the distinct BS channel estimates. Then, in step 2306, a channelestimation boundary switching module within the WT transmitter signalprocessing chain is operated to couple a first antenna element from aset of multiple antenna elements, e.g., a set of two antenna elements,to a single transmitter chain. Operation proceeds from step 2306 to step2308. In step 2308, the WT is operated to transmit an uplink signal tothe base station using the first antenna element, and in step 2310 theWT is operated to track the timing of the BS channel estimationscorresponding to the uplink signaling.

Operation proceeds from step 2310 to step 2312, where a check isperformed as to whether a channel estimation boundary is reached. If achannel estimation boundary is not reached operation proceeds to step2308, where the WT is operated to transmit an additional uplink signalusing the same antenna element, the first antenna element. However, ifit is determined in step 2312 that a channel estimation boundary wasreached, then operation proceeds from step 2312 to step 2314. In step2314, the channel estimation boundary switching module is operated toswitch from the first antenna element to the second antenna element.Operation proceeds from step 2314 to step 2316. In step 2316, the WT isoperated to transmit an uplink signal to the BS using the second antennaelement, and in step 2318 the WT is operated to track the timing of theBS channel estimations corresponding to uplink signaling.

Operation proceeds from step 2318 to step 2320, where a check isperformed as to whether a channel estimation boundary is reached. If achannel estimation boundary is not reached operation proceeds to step2316, where the WT is operated to transmit an additional uplink usingthe same antenna element, the second antenna element. However, if it isdetermined in step 2320 that a channel estimation boundary was reached,then operation proceeds from step 2320 to step 2322. In step 2322, thechannel estimation boundary switching module is operated to switch fromthe second antenna element to the first antenna element. Operationproceeds from step 2322 to step 2308, where the WT is operated totransmit an uplink signal to the BS using the first antenna element.

The operations of flowchart 2300 result in a predetermined and periodicswitching sequence between first and second antenna elements. Assumingthat the exemplary WT has only two transmitter antenna elements, theoperations of flowchart 2300 can result in uniform utilization ofantenna elements. In some embodiments, each of the antenna elements isoriented in a different direction. In some embodiments, the first andsecond antenna elements are spaced apart so that a differentcommunications path exists between each of the first and second antennaelements and the base station. In some embodiments, the spacing betweenantenna elements is at least ¼ of a wavelength of the lowest frequencytone transmitted from the antenna element.

The methods of flowchart 2300 can be extended to include embodimentswith more than two antenna elements. The method of flowchart 2300 iswell suited for both OFDM and CDMA applications. In some OFDMembodiments, channel estimation boundaries may correspond to dwellboundaries or multiples of dwell boundaries. In some CDMA embodiments,each of the different channel estimates may correspond to differentcodewords.

FIG. 24 is a flowchart 2400 of an exemplary method of operating a WT tocommunicate with a base station including performing channel estimationboundary switching of transmitter antenna elements, in accordance withthe present invention. The WT may be, e.g., an exemplary WT similar toor the same as WT 1600 of FIG. 18, and the base station may be, e.g., anexemplary BS similar to or the same as BS 1800 of FIG. 15. Operationstarts in step 2402 and proceeds to step 2404 and step 2416 in parallel.In step 2404 a channel estimation boundary switching module within theWT transmitter signal processing chain is operated to couple the singletransmitter chain of the WT to a designated antenna element form a setof multiple antenna elements. Then, in step 2408, the WT is operated totrack the timing of the BS channel estimations corresponding to uplinksignaling. For example, based on some received downlink broadcastsignals from the base station, the WT obtains information used todetermine the timing of the base station with regard to its channelestimations of received uplink signaling, e.g., information definingboundaries between a plurality of channel estimates being performedand/or information defining boundaries defining initialization or resetsof channel estimates. For example, consider an exemplary embodimentwhere the BS performs a channel estimate of received uplink signalingwhich it uses for a fixed interval, reinitializes the estimate filter,and then starts another estimate which it uses for a subsequent intervalof the same duration, and periodically repeats this method of channelestimation. Broadcast timing information from the BS may allow the WT tosynchronize its uplink signaling with these channel estimationboundaries. Operation proceeds from step 2408 to step 2410 where a checkis performed as to whether a channel estimation boundary is reached. Ifa channel estimation boundary has not been reached, then operationproceeds from step 2410 to step 2412. In step 2412, the WT is operatedto transmit an uplink signal to the BS, and operation returns to step2408. However, if a channel estimation boundary was reached in step2410, then operation proceeds to step 2414, where the WT is operated tomake an antenna element switching decision as a function of receivedfeedback signals.

Returning to step 2416, in step 2416, the WT is operated to receive afeedback signal or signals from the base station, the feedback signal orsignals indicative of channel quality of the received uplink signals.The feedback signal or signals indicative of channel quality of receiveduplink signals including at least one of a transmission power controlsignal indicating WT uplink power control information and a transmissionacknowledgement signal indicating success or failure in receipt oftransmitted uplink signal or signals. Operation proceeds from step 2416to step 2418. In step 2418, the WT is operated to correlate the receivedsignal or signals to an antenna element used and update a set offeedback information corresponding to that antenna element. The basestation, which sent the feedback information, need not, and in manyembodiments, does not know which antenna element was used fortransmission of the uplink signals corresponding to that channelestimation, the WT performing the tracking and matching of antennaelements used with received feedback information. The information ofstep 2418 is made available to the WT to be used in making the antennaelement switching decision of step 2414.

In step 2414, quality indicator information corresponding to thecurrently selected antenna element may be compared to thresholds usedfor maintaining the connection. Quality indicator informationcorresponding to the set of candidate replacement antenna elements maybe used to determine which antenna element to select when a decision hasbeen made to switch. In addition, in some embodiments, switching may beperformed, e.g., periodically, between antenna elements, irrespective orwith minimal concern for the stored channel quality information, for thepurposes of obtaining new channel quality information and evaluatingalternate channels corresponding to alternate antenna elements.Operation proceeds from step 2414 to step 2420.

If in step 2414, a decision has been made to remain on the currentlyselected antenna element, then operation proceeds from step 2420 to step2412, where the WT is operated to transmit an uplink signal to the BS.However, if the WT has decided to switch transmitter antenna elements,then operation proceeds from step 2420 to step 2422. In step 2422, theWT is operated to update and maintain switching control information setscorresponding to different antenna elements, e.g., setting a control bitcorresponding to activation of the newly selected antenna element andclearing a control bit corresponding to the previously used antennaelement. Then, in step 2424, the channel boundary switching module isoperated to switch the designated antenna element used for transmissionto a different antenna element from the set of multiple antennaelements, e.g., the antenna element selected in step 2414 and configuredfor in step 2422. In accordance with the invention, switching iscontrolled to be performed at signal boundaries corresponding to basestation channel estimation signal boundaries, but not in-between.Operation proceeds form step 2224 to step 2426.

In step 2426, the WT is operated to transmit an uplink signal to thebase station thru the designated antenna element. Operation proceedsfrom step 2426 to step 2408.

The method of flowchart 2400 is well suited for both OFDM and CDMAapplications. In some OFDM embodiments, channel estimation boundariesmay correspond to dwell boundaries or multiples of dwell boundaries. Insome OFDM embodiments, each channel estimation signal interval includesmultiple OFDM symbol transmission time periods and the tones used the WTin each channel estimation signal interval are determined according to atone hopping sequence. In some CDMA embodiments, each of the differentchannel estimates may correspond to different codewords.

In some embodiments, each of the antenna elements is oriented in adifferent direction. In some embodiments, the first and second antennaelements are spaced apart so that a different communications path existsbetween each of the first and second antenna elements and the basestation. In some embodiments, the spacing between antenna elements is atleast ¼ of a wavelength of the lowest frequency tone transmitted fromthe antenna element.

FIG. 25 is a flowchart 2500 of an exemplary method of operating anexemplary OFDM communications device, e.g., an exemplary WT similar toor the same as WT 1700 of FIG. 18, including assigning different tonesubsets to different antenna elements and transmitting over multipleantenna elements in parallel, in accordance with the present invention.Operation starts in step 2502 and proceeds to step 2504. In step 2504,the communications device is operated to assign tones in a first set oftones to a plurality of different tone subsets including at least afirst and a second tone subset, each of said different tone subsetsbeing different form one another by at least one tone. In someembodiments, the tones assigned to the first and second tone subset aremutually exclusive. Operation proceeds from step 2504 to step 2506. Instep 2506, the communications device is operated to transmit each ofsaid different tone subsets in parallel during the same time intervalusing a different antenna element for each of said different tonesubsets. Operation proceeds from step 2506 to step 2508, where thecommunications device changes the number of tones assigned to at leastone of the first and second tone subsets. Operation proceeds from step2508 back to step 2504. In some embodiment, the assignment of toneschanges on a periodic basis.

In some embodiments, the communications device of the flowchart 2500 isa wireless terminal transmitting uplink signals, e.g., uplink signalsusing tones which are hopped according to an uplink hopping sequence ona dwell by dwell basis, to a base station, and the base station receivesthe uplink signals. In other embodiments, the communications device ofthe flowchart 2500 is a base station, e.g., similar to or the same asexemplary BS 1900 of FIG. 16, transmitting downlink signals, e.g.,downlink signals using tones which are hopped according to a downlinkhopping sequence for each OFDM symbol transmission time interval, and awireless terminal receives the downlink signals.

FIG. 26 is a flowchart 2600 of an exemplary method of operating anexemplary OFDM communications device, e.g., an exemplary WT similar toor the same as WT 1700 of FIG. 19, including receiving and processingchannel quality indicator information, assigning different tone subsetsto different antenna elements, and transmitting over multiple antennaelements in parallel, in accordance with the present invention.Operation starts in step 2602 and proceeds to step 2604. In step 2604,the communications device is operated to assign tones in a first set oftones to a plurality of different tone subsets including at least afirst and a second tone subset, each of said different tone subsetsbeing different from one another by at least one tone. In someembodiments, the assignment of tones changes on a periodic basis.Operation proceeds from step 2604 to step 2606, where the communicationsdevice is operated to transmit each of said different tone subsets inparallel during the same time interval using a different antenna elementfor each of said different tone subsets, said different antenna elementsincluding at least a first and second antenna element. Operationproceeds from step 2606 to step 2608. In step 2608, the communicationsdevice is operated to receive a signal or signals indicative of channelquality including at least one of a transmission power control signalindicative of the communication device transmission power and atransmission acknowledgement signal indicating success or failure in thereceipt of a communication device transmitted signal or signals.

Then, in step 2610, based on the received quality indicator information,the communications device decides whether or not the allocation of tonesto tone subsets should be changed. For example, if there is insufficientquality indicator information stored to make a reasonable judgment as towhich antenna element has better channel quality and should be favored,then the communications device may decide to change the allocation oftones to favor one antenna, such that quality indicator feedbackinformation may be collected with a high weighting toward an individualantenna element, and the communications device may periodically cyclethrough each of the antenna elements. If sufficient information existsto make a tone allocation decision, the communications device can decideto change allocation of tones to tone subsets to attempt to achieve morefavorable channel conditions, e.g., changes resulting in a lower WTtransmission power level to achieve the same ack/nak ratio, changesresulting in an improved ack/nak ration, and/or changes resulting inlower communications device transmission power levels. If it is decidedin step 2610 not to change the allocation of tones to tone subsets, thenoperation returns to step 2604. However, if it is decided in step 2610that the allocation of tones to tone subsets should be changed, thenoperation proceeds to step 2612, where the communications device isoperated to change the number of tones in at least one of the first andsecond tone subsets. In some embodiments, the first tone subset isallocated a plurality of tones and the second tone subset is allocatedzero tones. Operation proceeds from step 2612 to step 2604.

In some embodiments, the tone allocation is performed as a function ofmultiple signals received from the device communicating with thecommunications device and the method includes maintaining different setsof tone allocation control information for signals received from saiddevice communicating with said communications device corresponding tosignals transmitted from said communications device using differentantenna elements.

In some embodiments, the communications device of the flowchart 2600 isa wireless terminal transmitting uplink signals, e.g., uplink signalsusing tones which are hopped according to an uplink hopping sequence ona dwell by dwell basis, to a base station, and a base station receivesthe uplink signals and transmits feedback channel quality signals. Inother embodiments, the communications device of the flowchart 2600 is abase station, e.g. BS 1900 of FIG. 16, transmitting downlink signals,e.g., downlink signals using tones which are hopped according to adownlink hopping sequence for each OFDM symbol transmission timeinterval, and a wireless terminal receives the downlink signals andtransmits feedback channel quality signals.

The invention will now be described further. While portions of thefollowing discussion may repeat some of the above discussion, featuresof some embodiments are discussed in greater detail. As discussed above,the invention uses a novel technique that enables a mobile transmitterto realize uplink transmit diversity without any significant cost orcomplexity using a single RF chain and multiple physical antennas.

For the sake of illustration, consider the invention in the context ofthe spread spectrum OFDM (orthogonal frequency division multiplexing)multiple-access system. Note that the present transmit diversitytechnique is applicable to other systems as well.

In the exemplary OFDM system, tones hop to realize spread spectrumadvantages. In the downlink (from the base station to the wirelessterminal), tones hop every OFDM symbol. Every logical tone is mapped toa different physical tone and this mapping is varied on every OFDMsymbol boundary. This hopping ensures that a coding block including somesubset of logical tones is spread across the entire available frequencyband. In the uplink (from the wireless terminal to the base station),every logical tone is mapped to a physical tone with the mapping heldconstant for a few OFDM symbol periods. This duration is known as adwell period. The process of uplink hopping across dwell periods isillustrated in 5.

The invention can be used at the transmitter of the wireless terminal toachieve transmit diversity in the cellular uplink. The inventionrequires the mobile transmitter to have multiple physical transmitantennas, but does not require it to include multiple RF chains. Apreferred embodiment of the invention is to switch the transmit antennasat the dwell boundaries of the uplink signal.

To illustrate this, consider FIG. 6, which illustrates a codeword beingtransmitted on the uplink over four successive dwell periods. Assumethat the mobile transmitter has two physical transmit antennas and asingle RF chain as illustrated in FIG. 3. While the transmitterillustrated in FIG. 3 is representative of any system that usesselection diversity, this invention achieves transmit diversity on afast time-scale within a codeword. A switching module operating underdirection of a switching control module in the transmitter can directthe transmit signal through either of the transmit antennas. Theswitching control module in one embodiment is aware of dwellinformation. The switching control module may receive such informationand/or switching instructions from a baseband unit in the mobiletransmitter. The switching control module instructs the switching unitto transmit the codeword through antenna 1 in dwells 1 and 3, andantenna 2 in dwells 2 and 4. At the receiver, part of the coding blockexperiences the channel response H₁ from antenna 1, and part of itexperiences the response H₂ from antenna 2. In one exemplary OFDMsystem, the base station receiver does not assume any channel coherencefrom one dwell to another and estimates the channel independently withineach dwell. Thus, switching on dwell boundaries does not interfere withbase station channel estimates or necessitate additional estimates.Then, switching transmit antennas at the dwell boundaries does notaffect the operations carried out at the receiver. Indeed, in thissituation, the base station receiver may not even be aware of the use ofthe present transmit diversity invention. Assuming the channel responsesH₁ and H₂ are independent, the receiver may realize diversity gain overthe coding block.

In general, Let N denote the number of the transmit antennas at themobile transmitter and let {H_(k), k=1 . . . , N} denote the wirelesschannel response from each of the transmit antennas to the receiver. Thetransmit antennas are preferably spatially arranged in such a mannerthat the ensemble of channel responses, {H_(k)}, are substantiallyindependent. In some embodiments the antennas are spaced apart by morethan ½ the wavelength of a carrier frequency being used to transmit thesignals. In many cases antenna spacing is more than one carrierwavelength apart. By switching from one transmit antenna to another overthe length of a coding block, the effective channel response from thetransmitter to the receiver varies among {H_(k)}, therefore realizingtransmit diversity. As another generalization of the invention, thetransmitter may switch the antenna once every dwell or once every fewdwells.

In the above descriptions, the switching block at the transmitterchooses each of the transmit antennas substantially equally. However,non-equal use of antennas is possible. In some embodiments the basestation provides channel feedback information to the mobile indicatingthe quality of the uplink channels corresponding to the differentantennas being used. The mobile responds to used information bycontrolling the switching module to cause the antenna or antennascorresponding to the better channel(s) to be used more than the antennaswhich correspond to lower quality channels. Suppose that the basestation the receiver feeds back some indication of the channel qualityto the transmitter. The transmitter can find out which transmit antennaresults in better channel quality and choose to either use that antennafor a substantial fraction of the time. The transmitter normallycontinues to use the antenna that is known to be less desirable for atleast some period of time in order that the base station receiver maymonitor changing channel conditions. The base station may then instructthe mobile transmitter to switch the antennas according to thetime-varying channel conditions. The feedback and antenna channelselection technique is particularly useful where channel conditions varyslowly, e.g., remain constant over multiple dwells. Such conditions maybe encountered, e.g., in cases where a wireless terminal remainsstationary for a period of time, e.g., while a person is working fromthe same location for the duration of a communications session.

This inventive form of realizing transmit diversity at the mobiletransmitter may be coupled with traditional forms of realizing receivediversity at the base station receiver as well to yield additionaldiversity gains.

This embodiment of the invention is particularly valuable in the contextof the cellular uplink since it requires a single RF chain at thetransmitter. This substantially reduces the cost and complexity ofrealizing transmit diversity gains on a mobile device.

Various aspects of uplink transmit diversity using tone-splitting shallnow be further described. Various embodiments of the proposed inventionalso incorporates another technique to achieve uplink transmit diversityin the context of the exemplary OFDM multiple-access system. Thisembodiment of the invention requires the mobile transmitter tosimultaneously transmit information using more than one transmitantenna.

For the sake of illustration, consider a mobile transmitter that has twotransmit antennas. A subset of tones in each OFDM symbol is transmittedthrough the first antenna, with the remaining set of tones beingtransmitted through the second antenna as illustrated in FIG. 9. In theexemplary OFDM system, the uplink hopping sequence that maps logical tophysical tones is varied on dwell boundaries. Therefore, the subset oftones that are transmitted through each antenna is kept fixed for theentire dwell, thus maintaining channel coherence at the receiver. Onceagain, the base station receiver does not need to be explicitly aware ofthe tones being split among the different antenna at the transmitter.

When a codeword is transmitted over several dwell periods in thismanner, diversity gain is realized at the receiver since different partsof the codeword are received over different channels corresponding tothe responses from the multiple transmit antennas.

There can be several different motivations to determine the tonesplitting. Tones may be split in a manner that maximizes the diversitygain for a particular uplink channel. Another motivation may be tominimize the peak-to-average ratio for any of the power amplifiersdriving each of the antennas.

A practical benefit of the tone-splitting benefit is the ability totransmit at higher power without disproportionately increased cost. Inthe embodiment of this invention that uses two transmit antennas, thepower amplifiers driving the antennas can be rated at 1 W (watt) each,leading to a total power of 2 W (watts). This is typically much lower incost when compared to a single power amplifier that is rated at 2 W(watts).

This technique can be generalized easily to multiple antennas. Eachphysical transmit antenna is coupled to an RF chain as illustrated inFIG. 27. FIG. 27 is a drawing 2700 illustrating an exemplary transmitterconfiguration which may be used in tone-splitting embodiments of thepresent invention. The exemplary transmitter of FIG. 27 includes asingle baseband unit 2706 and a single frequency transmit splittingcontrol module 2704. The baseband unit 2706 receives information totransmit 2702, e.g., encoded user data, and control signals from thefrequency transmit splitting control module 2704. The information 2702is mapped to a set of tones to be used for transmission. Differentsubsets of tones are formed from the set of tones, the different tonesubsets being different from one another by at least one tone. In someembodiments, the different subsets of tones are mutually exclusive. Insome embodiments, tone subsets may overlap. In some embodiments, thenumber of tones in each subset are the same. In some embodiments, thenumber of tones in one tone subset is controlled to be different thanthe number of tones in another tone subset. In some embodiments some ofthe tone subsets are null sets. The control signals from the frequencytransmit splitting control module 2704 determine the characteristics ofthe tone subsets, e.g., number and selection of tones in a given tonesubset, and identifies each tone subset with a specific transmitchain/transmit antenna at specified time intervals. The baseband module2706 outputs signals to a plurality of transmit chains (transmit chain 12707, transmit chain N 2707′). Information 2702 input to the basebandunit 2706 is routed to one or more of the transmit chains 2707, 2707′ asa function of control signals from the frequency transmit splittingcontrol module 2704. For a given OFDM symbol transmission time interval,the baseband unit 2706 maps the information bits to be transmitted to aset of tones to be used for transmission, and then identifies subsets oftones with its associated transmitter chain/transmitter antenna(2707/2114, 2707′/2714′) pair; this information is conveyed in a digitalformat to the digital signal processing modules (2708, 2708′). Eachtransmit chain (2707, 2707′) includes a digital signal processing block(2708, 2708′), a digital-to-analog conversion block (2710, 2710′), andan analog signal processing block (2712, 2712′), respectively. Thedigital signal processing blocks (2708, 2708′) converts the receivedinformation to digital signals to be communicated. The digital-to-analogconversion modules (2710, 2710′) convert the digital signals to analogsignals, e.g., analog modulation symbols on selected tones orsub-carrier frequencies using a selected carrier frequency, and theanalog signal processing chain (2712, 2712′) performs additional analogsignal processing, e.g., amplifying and filtering the signal to betransmitted. Each analog signal processing block (2712, 2712′) iscoupled to a transmit antenna (transmit antenna 1 2714, transmit antennaN 2714′), respectively. Different the analog signals are transmittedthrough a plurality of antennas (transmit antenna 1 2714, transmitantenna N 2714′) simultaneously, the composite of the analog signalsincluding the set of original encoded information bits included ininformation 2702.

FIG. 28 is a drawing 2800 illustrating another exemplary transmitterconfiguration which may be used in tone-splitting embodiments of thepresent invention. The various elements (2802, 2804, 2806, 2810, 2812,2814, 2810′, 2812′, 2814′) of FIG. 28 are similar or the same aselements (2702, 2704, 2706, 2710, 2712, 2714, 2710′, 2712′, 2714′),respectively, of FIG. 27 which have been previously described.Transmitter chain 1 2807 and transmitter chain N 2807′ of FIG. 28 aresimilar to chains (2707, 2707′) of FIG. 27; however, chains 2807 and2807′ share a common digital signal processing block 2808. The commondigital signal processing block 2808 performs both the functions ofdigital signal processing block 2708 and 2708′, e.g., on a time sharedbasis, providing efficiencies in terms of hardware cost, reduced weight,reduced size, and/or lower power consumption.

FIG. 29 is a drawing 2900 illustrating another exemplary transmitterconfiguration which may be used in tone-splitting embodiments of thepresent invention. The various elements (2902, 2906, 2908, 2910, 2912,2808′, 2810′, 2812′) of FIG. 29 are similar or the same as elements(2702, 2706, 2708, 2710, 2712, 2708′, 2710′, 2712′), respectively, ofFIG. 27 which have been previously described. The transmitter 2900 ofFIG. 29 includes two transmit chains (transmit chain 1 2907, transmitchain 2 2907″), while the transmitter 2700 of FIG. 27 includes Ntransmitter chains. Both transmitter 2700 and transmitter 2900 include Nantennas or antenna elements. The transmitter 2900 of FIG. 29 uses anadditional antenna switching module 2813 to couple two of the antennas(antenna 1 2914, antenna 2 2914″, antenna N 2914′) to the transmitterchains at any given time. As shown in FIG. 29, transmit chain 1 2907 ispresently coupled to transmit antenna 2 2914″, while transmit antenna N2914′ is coupled to transmit chain 2 2907″. Frequency transmit splittingcontrol module 2904, in addition to performing the function of module2904 of FIG. 27, performs selection and control of antenna matching totransmit chain, and module 2904 sends control signals to the switchingmodule 2913.

In some embodiments, the plurality of antennas or antenna elements usedto obtain diversity, in accordance with the methods of the presentinvention, may be mounted or situated remotely from the mobilecommunications device, e.g., at different locations on a vehicle.

While described in the context of an OFDM system, the methods andapparatus of the present invention, are applicable to a wide range ofcommunications systems including many non-OFDM and/or non-cellularsystems.

In various embodiments nodes described herein are implemented using oneor more modules to perform the steps corresponding to one or moremethods of the present invention, for example, signal processing,antenna switching, message generation and/or transmission steps. In someembodiments various features of the present invention are implementedusing modules. Such modules may be implemented using software, hardwareor a combination of software and hardware. Many of the above describedmethods or method steps can be implemented using machine executableinstructions, such as software, included in a machine readable mediumsuch as a memory device, e.g., RAM, floppy disk, etc. to control amachine, e.g., general purpose computer with or without additionalhardware, to implement all or portions of the above described methods,e.g., in one or more nodes. Accordingly, among other things, the presentinvention is directed to a machine-readable medium including machineexecutable instructions for causing a machine, e.g., processor andassociated hardware, to perform one or more of the steps of theabove-described method(s).

Numerous additional variations on the methods and apparatus of thepresent invention described above will be apparent to those skilled inthe art in view of the above description of the invention. Suchvariations are to be considered within the scope of the invention. Themethods and apparatus of the present invention may be, and in variousembodiments are, used with CDMA, orthogonal frequency divisionmultiplexing (OFDM), and/or various other types of communicationstechniques which may be used to provide wireless communications linksbetween access nodes and mobile nodes. In some embodiments the accessnodes are implemented as base stations which establish communicationslinks with mobile nodes using OFDM and/or CDMA. In various embodimentsthe mobile nodes are implemented as notebook computers, personal dataassistants (PDAs), or other portable devices includingreceiver/transmitter circuits and logic and/or routines, forimplementing the methods of the present invention.

1. A wireless terminal for use in a communication system including abase station, the wireless terminal comprising: a transmitter signalprocessing chain including a switching module for coupling saidtransmitter chain to a plurality of antenna elements, said switchingmodule configured to perform switching on signal boundariescorresponding to base station channel estimation memory reset points butnot in between, said plurality of antenna elements including at least afirst antenna element and a second antenna element each of which can beused independently; and a switching control module configured to controlthe switching module during a first period of time to switch betweensaid first and second antenna elements on at least some signalboundaries corresponding to base station channel estimation memory resetpoints which occur during said first period of time to thereby changethe antenna element used to transmit signals from said transmittersignal processing chain, each switch, during said first period of time,being preceded and followed by at least one dwell, a dwell being aperiod of time during which said wireless terminal uses a single set oftones to transmit signals to said base station, a different set of tonesbeing used in immediately consecutive dwells during said first period oftime.
 2. The wireless terminal of claim 1, wherein said switching moduleswitches between said first and second antenna elements according to apredetermined switching sequence.
 3. The wireless terminal of claim 1,wherein said transmitter signal processing chain is an orthogonalfrequency division multiplexing (OFDM) signal processing chain.
 4. Awireless terminal for use in a communication system including a basestation, the wireless terminal comprising: a transmitter signalprocessing chain including switching means for coupling said transmitterchain to a plurality of antenna elements, said switching means switchingon signal boundaries corresponding to base station channel estimationmemory reset points but not in between, said plurality of antennaelements including at least a first antenna element and a second antennaelement each of which can be used independently; and switching controlmeans for controlling the switching means during a first period of timeto switch between said first and second antenna elements on at leastsome signal boundaries corresponding to base station channel estimationmemory reset points which occur during said first period of time tothereby change the antenna element used to transmit signals from saidsingle transmitter signal processing chain, each switch during saidfirst period of time being preceded and followed by at least one dwell,a dwell being a period of time during which said wireless terminal usesa single set of tones to transmit signals to said base station, adifferent set of tones being used in immediately consecutive dwellsduring said first period of time.
 5. The wireless terminal of claim 4,wherein said switching means switches between said first and secondantenna elements according to a predetermined switching sequence.
 6. Thewireless terminal of claim 4, wherein said transmitter signal processingchain is an orthogonal frequency division multiplexing (OFDM) signalprocessing chain.
 7. A computer readable medium including machineexecutable instructions, for use in a wireless terminal in acommunication system including a base station, said wireless terminalincluding a transmitter signal processing chain including a switchingmodule for coupling said single transmitter chain to a plurality ofantenna elements, the computer readable medium comprising: instructionsfor causing said switching module to perform switching on signalboundaries corresponding to base station channel estimation memory resetpoints but not in between, said plurality of antenna elements includingat least a first antenna element and a second antenna element each ofwhich can be used independently; and instructions for causing theswitching module, during a first period of time, to switch between saidfirst and second antenna elements on at least some signal boundariescorresponding to base station channel estimation memory reset pointswhich occur during said first period of time to thereby change theantenna element used to transmit signals from said single transmittersignal processing chain, each switch during said first period of timebeing preceded and followed by at least one dwell, a dwell being aperiod of time during which said wireless terminal uses a single set oftones to transmit signals to said base station, a different set of tonesbeing used in immediately consecutive dwells during said first period oftime.
 8. A wireless terminal for use in a communications systemincluding a base station, said wireless terminal the comprising: atransmitter processing chain including a switching module for couplingsaid transmitter processing chain to a plurality of antenna elements,said switching module configured to switch on signal boundariescorresponding to base station channel estimation reset points but not inbetween, a base station channel estimation reset point being a signalpoint where said base station transitions between channel estimationintervals and resets a channel estimate included in the base station,the channel estimation performed by a base station in a channelestimation interval immediately preceding a channel reset beingindependent of the channel estimation performed in a subsequent channelestimation interval immediately following the channel estimate reset,said plurality of antenna elements including at least a first antennaelement and a second antenna element each of which can be usedindependently; and a switching control module configured to control theswitching module during a first period of time to switch between saidfirst and second antenna elements on at least some signal boundariescorresponding to base station channel estimation reset points whichoccur during said first period of time to thereby change the antennaelement used to transmit signals from said transmitter signal processingchain.
 9. The wireless terminal of claim 8, wherein said switchingmodule switches between said first and second antenna elements accordingto a predetermined switching sequence.
 10. The wireless terminal ofclaim 8, wherein said transmitter processing chain is an orthogonalfrequency division multiplexing (OFDM) signal processing chain.
 11. Awireless terminal for use in a communications system including a basestation, said wireless terminal the comprising: a transmitter processingchain including switching means for coupling said transmitter processingchain to a plurality of antenna elements, said switching means switchingon signal boundaries corresponding to base station channel estimationreset points but not in between, a base station channel estimation resetpoint being a signal point where said base station transitions betweenchannel estimation intervals and resets a channel estimate included inthe base station, the channel estimation performed by a base station ina channel estimation interval immediately preceding a channel resetbeing independent of the channel estimation performed in a subsequentchannel estimation interval immediately following the channel estimatereset, said plurality of antenna elements including at least a firstantenna element and a second antenna element each of which can be usedindependently; and switching control means for controlling the switchingmeans, during a first period of time, to switch between said first andsecond antenna elements on at least some signal boundaries correspondingto base station channel estimation reset points which occur during saidfirst period of time to thereby change the antenna element used totransmit signals from said transmitter signal processing chain.
 12. Thewireless terminal of claim 11, wherein said switching means switchesbetween said first and second antenna elements according to apredetermined switching sequence.
 13. The wireless terminal of claim 11,wherein said transmitter processing chain is an orthogonal frequencydivision multiplexing (OFDM) signal processing chain.
 14. A computerreadable medium including machine executable instructions, for use in awireless terminal in a communications system including a base station,said wireless terminal including a transmitter processing chainincluding a switching module for coupling said transmitter processingchain to a plurality of antenna elements, the computer readable mediumcomprising: instructions for causing the switching module to switch onsignal boundaries corresponding to base station channel estimation resetpoints but not in between, a base station channel estimation reset pointbeing a signal point where said base station transitions between channelestimation intervals and resets a channel estimate included in the basestation, the channel estimation performed by a base station in a channelestimation interval immediately preceding a channel reset beingindependent of the channel estimation performed in a subsequent channelestimation interval immediately following the channel estimate reset,said plurality of antenna elements including at least a first antennaelement and a second antenna element each of which can be usedindependently; and instructions for causing the switching module to,during a first period of time, switch between said first and secondantenna elements on at least some signal boundaries corresponding tobase station channel estimation reset points which occur during saidfirst period of time to thereby change the antenna element used totransmit signals from said single transmitter signal processing chain.